Kill spurious errors from one side legitimately closing the connection; we

Kill spurious errors from one side legitimately closing the connection; we
couldn't see these before, but with the upcoming change to log errors,
they fill the log with noise.

One more bogus SVN_ERR_RA_SVN_CONNECTION_CLOSED remains, that I have not
been able to track down.  It only manifests under authz_tests.py 13 (authz
issue #2712), so not so bad.

* subversion/include/svn_ra_svn.h
  (svn_ra_svn_handle_commands2): Add rev'd interface.

* subversion/libsvn_ra_svn/editorp.c
  (svn_ra_svn_drive_editor2): While discarding edit commands after
    sending the other side an error, don't consider it an error if the
    other side drops the connection.

* subversion/libsvn_ra_svn/marshal.c
  (svn_ra_svn_handle_commands2): Rev from svn_ra_svn_handle_commands,
    adding error_on_disconnect argument, and suppress
    SVN_ERR_RA_SVN_CONNECTION_CLOSED errors unless it is TRUE.

* subversion/svnserve/serve.c
  (accept_report): Use svn_ra_svn_handle_commands2, with
    error_on_disconnect TRUE.
  (serve): Use svn_ra_svn_handle_commands2, with error_on_disconnect FALSE;
    dropping the connection is proper when the client is done.

* subversion/svnserve/main.c
  (main): Don't ignore SVN_ERR_RA_SVN_CONNECTION_CLOSED errors here.  We
    have no idea here whether it was a real error or not!  The ones that
    are not real errors are now suppressed in the right places.

git-svn-id: http://svn.collab.net/repos/svn/trunk@30826 612f8ebc-c883-4be0-9ee0-a4e9ef946e3a