#20 blender2cal3d_2.py bug fix and enhancement

[Anonymous]

Running blender2cal3d_2.py more than once per
invocation creates empty skeleton files. This is
because BONES is not cleared each run. This patch
includes a fix to call BONES.clear() in the export
function to fix this problem.

This patch also includes the addition of a toggle
button that will force the export of submeshes into
their own .[xc]mf file. This is useful for apply
multiple textures to single meshes in environments that
don't support multiple textures per mesh.

[Nobody/Anonymous]

Patch to blender2cal3d_2.py for bug fix and enhancement