This adds support for the new-ish options:

QUATERNION
B_BONE_REST
INVERT_VERTGROUP
MULTIMODIFIER

to the bpy armature modifier API.

It also fixes a significant problem - In the docs, it refers to 
the 'VERTGROUP' field as being a string value, shared
by lattice, armature, etc, referring to the 'VGroup' field in the 
armature modifier that defines a vertex group 'mask'
which the armature's effect is restricted to.

However, previously, for some very mistaken reason, in processing 
the getters/setters for the armature modifier, the
VERTGROUP field was pointing to the quite different 'Vert. Groups' 
toggle in the armature modifier, that enables or
disables using vertex groups for deformation (as opposed to 
envelopes).

I've fixed this, so VERTGROUP points to the VGroup string, as is 
already defined in the docs and consistent with other
modifiers like Lattice. A new field: 'VGROUPS' has been added, 
which is the analog to the 'Vert Groups' toggle.

source/blender/python/api2_2x/doc/Modifier.py

@@ -93,7 +93,12 @@ Example::
 	- SCALE_VEC - Used for Array only (3d Vector)
 	- MERGE_DIST - Used for Array only (float)
 
+	- INVERT_VERTGROUP - Used for Armature only (bool)
 	- ENVELOPES - Used for Armature only (bool)
+	- VGROUPS - Used for Armature only (bool)
+	- QUATERNION - Used for Armature only (bool)
+	- B_BONE_REST - Used for Armature only (bool)
+	- MULTIMODIFIER - Used for Armature only (bool)
 	
 	- START - Used for Build only (int)
 	- SEED - Used for Build only (int)