Introduce SVNCompressionLevel mod_dav_svn parameter to make its
features symmetric to svnserve's. However, it seems that serf never
uses svndiff1 and compression is never done.
* subversion/mod_dav_svn/dav_svn.h
(dav_svn__get_compression_level): get the compression level setting
* subversion/mod_dav_svn/mod_dav_svn.c
(svn__compression_level): global compression level setting
(SVNCompressionLevel_cmd): process compression level config setting
(dav_svn__get_compression_level): implement
(cmds): declare SVNCompressionLevel config parameter
* subversion/libsvn_ra_neon/commit.c
(commit_apply_txdelta): use user-defined compression level
git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/integrate-compression-level@1072287 13f79535-47bb-0310-9956-ffa450edef68