fuzz: add support for fuzzing under either Python 2 or 3
This was more of a hairball than I hoped, but it appears to work. The hg-py3
branch of my oss-fuzz fork on github has the remaining changes to switch us to
Python 3, but we may as well retain Python 2 fuzzing support for at least a
little while.
Differential Revision: https://phab.mercurial-scm.org/D7592
#require execbit
$ hg init repo
$ cd repo
$ echo foo > foo
$ chmod 644 foo
$ hg ci -qAm '644'
$ chmod 755 foo
$ hg ci -qAm '755'
reverting to rev 0
$ hg revert -a -r 0
reverting foo
$ hg st
M foo
$ hg diff --git
diff --git a/foo b/foo
old mode 100755
new mode 100644
$ cd ..