* subversion/include/svn_string.h
  More docstring tweaks, adding missing @since tags, fixing other
  doxygen markup, and adding a summary to the new svn_stringbuf_replace()
  function.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1459448 13f79535-47bb-0310-9956-ffa450edef68