patch.diffopts: add support for noprefix
In an upcoming patch we'll enable support as an option to 'hg diff' as well.
The tests reflect the current state of the world -- as we add support we'll see
changes in the test output.
#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 ..