Prevent deadlocks on recursive calls (deleting communicators with
attributes from an attribute callback).

(cherry picked from commit 4d55ae838d5eff2818707da7ba60ffd640144360)
man: update a bunch of attribute-related man pages

Per discussion starting
http://www.open-mpi.org/community/lists/users/2014/12/26018.php, at
least note that OMPI does not allow adding or deleting attributes in
an attribute copy or delete callback (or any of its children) on the
same object on which the callback was invoked.

(cherry picked from commit 9144517ad420deb6bad1cb50c41ae74c35548ad0)
Merge pull request #142 from jsquyres/pr/attribute-sadness

Attribute "fixes"