Following up on r1446118, make the knowledge whether reversed obtaining of
file revisions is available visible by adding an ra capability.

This to allow a future blame improvement to decide whether it can use an
improved algorithm instead of the current one without waiting for an error
on old servers.

* subversion/include/svn_dav.h
  (SVN_DAV_NS_DAV_SVN_ATOMIC_REVPROPS): Move new in 1.7 define below one that
    exists in 1.6.
  (SVN_DAV_NS_DAV_SVN_INHERITED_PROPS): Mark new in 1.8.
  (SVN_DAV_NS_DAV_SVN_EPHEMERAL_TXNPROPS): Mark new in 1.8.
  (SVN_DAV_NS_DAV_SVN_INLINE_PROPS): Mark new in 1.8.
  (SVN_DAV_NS_DAV_SVN_GET_FILE_REVS_REVERSE): New macro.

* subversion/include/svn_ra.h
  (SVN_RA_CAPABILITY_GET_FILE_REVS_REVERSE): New macro.

* subversion/include/svn_ra_svn.h
  (SVN_RA_SVN_CAP_GET_FILE_REVS_REVERSE): New macro.

* subversion/libsvn_ra_local/ra_plugin.c
  (svn_ra_local__has_capability): Declare support for reversed file
    revisions *and* ephemeral txnprops.

* subversion/libsvn_ra_serf/options.c
  (capabilities_headers_iterator_callback): Forward
    SVN_RA_SVN_CAP_GET_FILE_REVS_REVERSE support.

* subversion/libsvn_ra_svn/client.c
  (ra_svn_has_capability): Make function table driven. Add
     SVN_RA_SVN_CAP_GET_FILE_REVS_REVERSE support.

* subversion/mod_dav_svn/version.c
  (get_vsn_options): Write SVN_DAV_NS_DAV_SVN_GET_FILE_REVS_REVERSE.

* subversion/svnserve/serve.c
  (serve): Send SVN_RA_SVN_CAP_GET_FILE_REVS_REVERSE support.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1446169 13f79535-47bb-0310-9956-ffa450edef68