Fix a misleading error message: "Unknown command: 'svn'".

* subversion/libsvn_ra_svn/editorp.c (svn_ra_svn_drive_editor2):
* subversion/libsvn_ra_svn/marshal.c (svn_ra_svn_handle_commands2):
    Say "Unknown editor command" instead.

* subversion/svn/svn.c (sub_main):
* subversion/svnadmin/svnadmin.c (sub_main):
* subversion/svndumpfilter/svndumpfilter.c (main):
* subversion/svnlook/svnlook.c (main):
* subversion/svnrdump/svnrdump.c (main):
* tools/client-side/svn-bench/svn-bench.c (sub_main):
* tools/dev/benchmarks/suite1/benchmark.py:
* tools/examples/svnshell.rb (SvnShell.dispatch):
* tools/server-side/svnauthz.c (sub_main):
    Say "Unknown subcommand" instead.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1435106 13f79535-47bb-0310-9956-ffa450edef68