Bunch of fixes for UI messages.

Also generate rigid body constraint types in py bullet code from RNA enum values (simpler than having to sync the code when something is changed here!).

Side note: RNA API about icons still needs to expose icons for enum values, and conversion funcs between icon_name and icon_value!

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54124 954f8c5b-7b00-dc11-b283-0030488c597c