ra_serf: Remove unneeded 'q=0.9' from Accept-Encoding request header value if there is only one accept encoding.
ra_serf: Remove unneeded 'q=0.9' from Accept-Encoding request header value if
there is only one accept encoding.

Suggested by: rhuijben

* subversion/libsvn_ra_serf/update.c
  (headers_fetch, setup_update_report_headers): Just use 'svndiff' as
   Accept-Encoding request header value if compression is disabled.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1710634 13f79535-47bb-0310-9956-ffa450edef68

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