Clarify comment.
Clarify comment.

* subversion/libsvn_ra_serf/ra_serf.h:
  (svn_ra_serf__xml_gather_since): tweak docstring for clarity

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