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

mercurial/util.py

@@ -17,6 +17,7 b' from __future__ import absolute_import'
 
 import bz2
 import calendar
+import codecs
 import collections
 import datetime
 import errno
@@ -2131,7 +2132,9 b' bytecount = unitcountfn('
     )
 
 def escapestr(s):
-    return s.encode('string_escape')
+    # call underlying function of s.encode('string_escape') directly for
+    # Python 3 compatibility
+    return codecs.escape_encode(s)[0]
 
 def uirepr(s):
     # Avoid double backslash in Windows path repr()