Matt Harbison <matt_harbison@yahoo.com> [Mon, 29 Jun 2015 10:34:56 -0400] rev 25689
revset: fix a crash in parents() when 'wdir()' is in the set
The crash was "TypeError: expected string or Unicode object, NoneType found"
down in revlog.parentrevs(). This fixes heads() too (which is where I found
it.)