Clear the scratch pool within the xml context. This also requires some debug code to ensure we haven't re-entered the context and might be claering an outer call's use of the pool.
Clear the scratch pool within the xml context. This also requires some
debug code to ensure we haven't re-entered the context and might be
claering an outer call's use of the pool.

* subversin/libsvn_ra_serf/xml.c:
  (START_CALLBACK, END_CALLBACK): helper macros to manipulate the
    debug-only flag within the context
  (svn_ra_serf__xml_context_t): add WITHIN_CALLBACK for debugging
  (svn_ra_serf__xml_cb_start, svn_ra_serf__xml_cb_end): wrap the
    callback invocation with callback flag markers. clear the scratch
    pool after the invocation.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1337689 13f79535-47bb-0310-9956-ffa450edef68

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