Another attempt to reduce the confusion between Object and Bone constraints

* The wording on the "Add Constraint" dropdown has been changed so that there is
no ambiguitiy about which tab is currently selected. That is, it now mentions
whether these are object or bone constraints, so that users don't need to try
and look up at the header to check.

* Show the warning about Ob vs Bone constraints when in armature editmode too.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55182 954f8c5b-7b00-dc11-b283-0030488c597c