Put Steve in a 1x1 hole and measure the wiggle room. ALL the room - WiggleRoom = Steve
In a 1x1 hole, I pointed the camera straight down and moved from corner to corner. Regardless of corner or orientation, the crosshairs pointed at the farthest point of a 5x5 square from the corner.
16 = 5 + 6 + 5
That's 16 total square width, 5 for the each side of Steve, and 6 for the wiggle room.
Front/back/left/right, the closest you can get to a wall is 5. This test is unable to confirm if Steve is 10x10 square, or a 5 radius circle.
Note: this finding contradicts the original question, as Steve is 0.625 wide, and the asker was expecting more than that. However the original question also supports this answer in the door screenshot (5 texture pixels from door).
It seems reasonable to think that Steve is an unrotating 0.625x0.625 square, which is 0.88 from corner to corner, and could not fit through the ~0.7 gap.
Here is Steve (in green), blocked by two stairs (in purple). Steve is 10 units big, but the yellow line is ~14.14 units big, which is too large to go through the ~11.3 unit opening.
![Steve trapped](https://i.stack.imgur.com/XjJMt.jpg)
According to the Minecraft Support Pages:
If you are playing version 1.3 or earlier, skin changes will not be reflected in-game.
Additionally, a message is shown near the skin upload field:
Note: Skin changes in Minecraft version 1.7.9 and future versions should happen immediately. If you are playing version 1.7.8 or an earlier version, skin changes may take up to an hour to be applied. If you are playing version 1.3 or earlier, skin changes will not be reflected in-game.
(emphasis mine)
This basically means you can't change your pre-1.3 skin anymore.
Best Answer
Simple Fix
Navigate to the minecraft profile page and click the "reset" button under "reset your skin".
(As pointed out by @Quinte in his answer)
Workaround
You can get the Steve Skin on Minecraft.net
In this case you will have a Steve skin.
Problems
Uploading the reference skin still counts as there being a skin, because, well, it is there. The problem here is that skins uploaded to the skin server take precedence over skins included in Resource Packs (e.g. the default skin in Sphax PureBDCraft).
Unfortunately there's no way to remove the skin from the skin-server completely.