py3: have registrar process docstrings in bytes
Mixing bytes and unicode creates a mess. Do things in bytes as possible.
New sysbytes() helper only takes care of ASCII characters, but avoids raising
nasty unicode exception. This is the same design principle as sysstr().
#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 ..