Armature with static object transform incorrectly exported

[bsupnik]

If an armature's "object" transform is non-animated, it is exported incorrectly. I tested a few cases:

• If the armature has a parent empty display with an offset or rotation, this parent's transform is ignored.
• If the armature itself has a rotation, the child mesh is correctly rotated, but the armature's rotation is not affected.

This bug also shows up when the entire setup is nested inside another animation.

I'm still investigating causes, but it appears to be caused by inconsistent handling of what should essentially be a 'bake matrix' for animations themselves. Some ad-hoc modification of the no-parent cases fixes this, but this fix may have introduced other bugs, and it won't fix the nested case.