stringutil: have buildrepr delegate to pprint for unknown types

This stabilizes some revset reprs across Python 2 and 3.

Differential Revision: https://phab.mercurial-scm.org/D4244

mercurial/utils/stringutil.py

@@ -114,7 +114,7 b' def buildrepr(r):'
     elif callable(r):
         return r()
     else:
-        return pycompat.byterepr(r)
+        return pprint(r)
 
 def binary(s):
     """return true if a string is binary data"""