[SalesForce] How to exclude invalid fields that can’t be deployed by the Migration Tool from .object files when automating deployment

I'm trying to add a level of automation to our development processes. My goal at the moment is to be able to automatically retrieve check-ins to our development feature release branch and then automatically deploy them into the QA Org for further testing. I've managed to get this all working with svn, the Migration Tool, and cruise control, but my main issue happens when including object definition files (e.g. Account.object) in the package when they have fields that can't be deployed.

I want to get away from new fields having to be setup manually or managed through change sets. It would be great to be able to include the Account.object file in the deployment package when there's been a new field added or modified so there doesn't have to be manually editing of the object file each time.

The problem with this approach is that there are multiple fields included in the .object definition that the Migration Tool can't/won't deploy. I get these error trying to deploy just our Account.object file to another Org:

BUILD FAILED
FAILURES:
Error: objects/Account.object(10881,15):Cannot modify managed object: entity=Web
Link, component=00b30000001pBPs, field=Url, state=MANAGED_INSTALLED: newValue='h
ttps://{URL A}
?sessionId={!API.Session_ID}
&serverUrl={!API.Partner_Server_URL_80}
&id={!Account.Id}', oldValue='{URL B}
?sessionId={!API.Session_ID}
&serverUrl={!API.Partner_Server_URL_80}
&id={!Account.Id}'
Error: objects/Account.object(10906,15):encodingKey must be specified
Error: objects/Account.object(10926,15):encodingKey must be specified
Error: objects/Account.object(10944,15):encodingKey must be specified
Error: objects/Account.object(10962,15):encodingKey must be specified
Error: objects/Account.object(10981,15):encodingKey must be specified
Error: objects/Account.object(11001,15):encodingKey must be specified
Error: objects/Account.object(11012,15):encodingKey must be specified
Error: objects/Account.object(11022,15):encodingKey must be specified
Error: objects/Account.object(11032,15):encodingKey must be specified
Error: objects/Account.object(11042,15):encodingKey must be specified
Error: objects/Account.object(11052,15):encodingKey must be specified
Error: objects/Account.object(11070,15):encodingKey must be specified
Error: objects/Account.object(11088,15):encodingKey must be specified
Error: objects/Account.object(11106,15):encodingKey must be specified
Error: objects/Account.object(11124,15):encodingKey must be specified
Error: objects/Account.object(11142,15):encodingKey must be specified
Error: objects/Account.object(11166,15):encodingKey must be specified
Error: objects/Account.object(11200,15):encodingKey must be specified
Error: objects/Account.object(11231,15):encodingKey must be specified
Error: objects/Account.object(11255,15):encodingKey must be specified
Error: objects/Account.object(11287,15):encodingKey must be specified
Error: objects/Account.object(11354,15):encodingKey must be specified
Error: objects/Account.object(11417,15):encodingKey must be specified
Error: objects/Account.object(3984,13):Field Segment__c is a picklist field. Pic
klist fields are only supported in certain functions. <a href="javascript:openPo
pupFocusEscapePounds('https://help.salesforce.com/apex/htdoor?loc=help&target=ti
ps_on_building_formulas.htm%23picklists_and_msps&section=Customizing&language=en
_US&release=182.8.1&instance=CS3', 'Help', 1024, 768, 'width=1024,height=768,res
izable=yes,toolbar=yes,status=yes,scrollbars=yes,menubar=yes,directories=no,loca
tion=yes,dependant=no', false, false);">Tell me more</a>

        at com.salesforce.ant.DeployTask.handleResponse(DeployTask.java:116)
        at com.salesforce.ant.SFDCMDAPIAntTaskRunner.runTask(SFDCMDAPIAntTaskRun
ner.java:94)
        at com.salesforce.ant.DeployTask.execute(DeployTask.java:59)
        at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:288)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:601)
        at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.jav
a:105)
        at org.apache.tools.ant.Task.perform(Task.java:348)
        at org.apache.tools.ant.Target.execute(Target.java:357)
        at org.apache.tools.ant.Target.performTasks(Target.java:385)
        at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1329)
        at org.apache.tools.ant.Project.executeTarget(Project.java:1298)
        at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExe
cutor.java:41)
        at org.apache.tools.ant.Project.executeTargets(Project.java:1181)
        at org.apache.tools.ant.Main.runBuild(Main.java:698)
        at org.apache.tools.ant.Main.startAnt(Main.java:199)
        at org.apache.tools.ant.launch.Launcher.run(Launcher.java:257)
        at org.apache.tools.ant.launch.Launcher.main(Launcher.java:104)

Total time: 25 seconds

So the first error appears to be because a managed field is different between the Development and QA Orgs (that's fine but I'd like to exclude it), then there's a shed load of "encoding key must be specified" errors, and finally a complaint about deploying a picklist definition.

So I'm wondering:

1. How do I exclude invalid fields (e.g. managed / picklist) from the
   .object file to make the deployment work? (Unless there's a way to
   deploy picklists?)
2. What does the "encoding key must be specified" error mean?

Thanks for your help

Ray