Fix T41871: F2 addon throws error if there is a material slot with no
material assigned to it

Reviewed By: sergey
FBX export: yet another attempt to fix scaling issues...

Still have the feeling many apps do not use UnitScaleFactor prop correctly, though. :/
FBX: correction to previous commit.

Better to use real Scale matrix than mere float multiplication here, I think.
Fix T42000: STL export scale incorrect.

Not a bug, in fact, more like a feature request.
Added an option to take into account scene's scale on both export and import time.

Also added scaling/axis conversion to importer.
STL import: Better to transform whole mesh at once, rather than each point in py.

Thanks Campbell for the headup.
Meeeh, cleanup (sorry for the noise :/ ).
Merged experimental code in 'stable' addon (mainly Jens Restemeier's summer work).

Will remove experimental one soon. Keeping old 6.1 exporter active for now, though.

Notes:
* Not 100% happy with how complex code is now... Rather sure though refactor would
  take a huge amount of time, not worth it for now.
* New code handles things like armature & animation import much much better than previous one,
  so definitively worth it.
* New code also fixes some real bugs (like Blender-side of T42135).
* Did a few cosmetic changes on the run, nothing serious.

This should make FBX work complete, aside from a few nice TODOs that I'll tackle in comming weeks,
in addition to ongoing bugbusting.

Many thanks to Jens for his work on armature mess! :D
FBX IO: remove experimental addon, now that 2.72 is out we moved everything to 'stable' one.
FBX Export: Fix typo in previous commit.
Fix T42135: FBX Exporter Armature not linked to mesh.

This time, it was exporter that did not support bone parenting of mere objects.

Also fixes a more general bug about parenting - matrix_parent_inverse
was not taken into account at all for child objects!
FBX Export: minor tweaks.

* Only export global animation if neither NLAStrips nor AllActions options are set.
* Do not prepend '_' to groups' filenames in case of batchexport with no prefix given.

Requested by Mango Jambo through mail.
fix warning with UI description
Fix T42171: Imprecise info in add curve/mesh extra object.
Fix T42190: FBX - script error when trying to export an animation without leaf-bones.
update bl_info & location text
fix typo in error report
fix warnings with UI description
Add missing 'bl_category' field to 3DView tool panel of rigify addon.
Add a few items to the view menu, now that nested pies are possible.
Fix minor error in previous commit