The popen2, sha and sets modules are deprecated in Python 2.6 (sha in
Python 2.5). Both popen2 and sha are not actually used in git-p4.
Replace usage of sets.Set with the builtin set object.
The built-in set object was added in Python 2.4 and is already used in
other parts of this script, so this dependency is nothing new.
Signed-off-by: Reilly Grant <reillyeon@qotw.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>