Following up on r1803899, properly negotiate the svndiff version when a client indicates the preference of svndiff2 format, but the compression is disabled on the server.
Following up on r1803899, properly negotiate the svndiff version when a
client indicates the preference of svndiff2 format, but the compression
is disabled on the server.

In this case, the server configuration should override the client's
preference (and this is how Subversion 1.9 worked), so tweak the
negotiation scheme so that the server would always be use uncompressed
svndiff0 format with "SVNCompressionLevel 0".

* subversion/mod_dav_svn/repos.c
  (negotiate_encoding_prefs): Add special handling for compression level 0.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1804822 13f79535-47bb-0310-9956-ffa450edef68

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