Improve utf conversion functions memory usage on Windows.
Improve utf conversion functions memory usage on Windows.

* subversion/libsvn_subr/win32_xlate.c
  (svn_subr__win32_xlate_to_stringbuf): Create stringbuf of
   required size at once instead of creating empty stringbuf and
   then extending to required size.

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