Fix T39755: recent patch which made ascii files write zero normals
FBX: After talk with Campbell, remove "simplify skinning" option.

This kind of target app compatibility feature is not well suited to an export addon,
would better be in a dedicated pre-export tool.
Add bl_category to 3DView panel.
Fix T39777: Blender 2.65-2.7 Sapling Bug

Clamp branchL to min 0.0 (negative branch length does not make much sense, and
non-int power of negative numbers gives complex numbers...).
Merge remote-tracking branch 'hm-blender/master'

* hm-blender/master:
  Fix T39777: Blender 2.65-2.7 Sapling Bug
  Add bl_category to 3DView panel.
  FBX: After talk with Campbell, remove "simplify skinning" option.
  Fix T39755: recent patch which made ascii files write zero normals
fixed: empty material slots
STL now always exports normals.

Normals are not optional for STL so remove the option from the UI.
Merge remote-tracking branch 'hm-blender/master'

* hm-blender/master:
  STL now always exports normals.
  fixed: empty material slots