De-duplicate the 'svn-check-*' targets of Makefile.svn. If we're going to use GNU-make-isms, we may as well get some good use out of them.
* tools/dev/unix-build/Makefile.svn (): Move PARALLEL to top of Makefile to make it more obvious that a user can override it from the command line. (svn-check-neon, svn-check-serf, svn-check-local, svn-check-svn): Move most of the logic into... (do_check): New macro. Functionally equivalent, except we now use mv instead of cp with the log files, to prevent copying an old one to a new destination.