cl: Unpleasant hack to fetch program name.

It seems that `cl-launch' doesn't set CL_LAUNCH_FILE when doing `-X',
which is rather inconvenient.  Stuff using `mdw.sys-base' wins because
(massive cheat) ASDF systems are loaded before the program name is
stripped off the front of the argument list; we don't get that luxury
here.  So `*load-pathname*' will have to do; take `pathname-name' to
strip away the unpleasant realities of FASL-caching.

Of course, if we're dumping images then CL_LAUNCH_FILE is set properly.
<sigh>