[Bf-python] Bug and Fix in tracker for Armature.NLA

[Roland Hess]

Armature.NLA.setName("foo") didn't check if "foo" already existed.  
You could end up with eight actions all named "foo".

Patch just reuses the name-check/increment code found elsewhere in  
the API.

http://projects.blender.org/tracker/? 
func=detail&aid=4171&group_id=9&atid=125

Roland Hess
harkyman