Blender export for version 2.63

[zilluss]

It seems that the API for Blender 2.63 has changed, and the export isn't working anymore. This commit fixes it. Please check if the change is correct, since this was my first time I worked with the Blender API.

[zilluss]

Forgot to mention: The change actually only affects the line 142 and changes
uv_layer = mesh.uv_textures.active
to
uv_layer = mesh.tessface_uv_textures.active

[endavid]

I tried this fix in 2.64 but it didn't work... I've posted a different version of the polygon export for v2.64 in this pull-request: #10