Simplify some mergeinfo code. No functional change.
Simplify some mergeinfo code. No functional change.

* subversion/libsvn_subr/mergeinfo.c
  (range_to_string): Return a simple "char *" string instead of setting an
    output pointer to an svn_string_t.
  (parse_revision_line, svn_rangelist_to_string): Adjust accordingly.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion