py3: call codecs.escape_encode() directly
string_escape doesn't exist on Python 3, but fortunately the undocumented
codecs.escape_encode() function exists on CPython 2.6, 2.7, 3.5 and PyPy 5.6.
So let's use it for now.
http://stackoverflow.com/a/23151714
#require unix-permissions no-root
$ hg init a
$ cd a
$ echo foo > b
$ hg add b
$ hg ci -m "b"
$ chmod -w .hg/store
$ cd ..
$ hg clone a b
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ chmod +w a/.hg/store # let test clean up
$ cd b
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
$ cd ..