Speed up svn:mergeinfo parser:  Most data in svn:mergeinfo is already
stored in normalized form.  In that case, there is no need to sort
and merge ranges.

* subversion/libsvn_subr/mergeinfo.c
  (is_rangelist_normalized): new utility function
  (parse_revision_line): perform normalization only when necessary


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1483309 13f79535-47bb-0310-9956-ffa450edef68