Short-circuit the UTF-8 conversion when the source encoding is UTF-8.  
Short-circuit the UTF-8 conversion when the source encoding is UTF-8.  

Do this by recognizing "UTF-8" as a magic number; that magic number (well,
magic string) is already used once in svnsync's normalize_string().  The
reason for the short-circuit is that the conversion would be a no-op; see
<http://mid.gmane.org/20130714165516.GA71250@minotaur.apache.org>.

This fixes svnsync_authz_tests.py 5 when apr_xlate_open() returns something
other than APR_SUCCESS in utf.c:xlate_alloc_handle().

* subversion/libsvn_subr/subst.c
  (svn_subst_translate_string2): As above.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1503009 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion