manifest: removed usage of the global cmp function

Py3k doesn't have a global cmp() function, making this call problematic in the
py3k port. Also, calling cmp() here is not necessary, since we only want to
know if the two values are equal. A check for equality perfect in this case and
this patch does that.

mercurial/manifest.py

@@ -84,7 +84,7 b' class manifest(revlog.revlog):'
                 hi = start
         end = advance(lo, '\0')
         found = m[lo:end]
-        if cmp(s, found) == 0:
+        if s == found:
             # we know that after the null there are 40 bytes of sha1
             end = advance(end + 40, '\n')
             return (lo, end + 1)