Let #'eval-after-load accept symbol for FILE arg

Let #'eval-after-load accept symbol for FILE arg

While looking into bug 183 I noticed that FSF's #'eval-after-load also
accepts a feature (i.e, a symbol) for the FILE arg.  I personally don't
think that's a wonderful idea, but I did see that a few things in
GNU/Emacs are using it (Tramp, for example).  This change adds rudimentary
support in our #'eval-after-load.  Basically, if FILE is a symbol, look up
a filename from #'feature-file, or use #'symbol-name if that fails.

The doc string was amended accordingly, and a note about the futility of
using #'eval-after-load with dumped lisp was also added.

	* lisp/subr.el (eval-after-load): Also accept symbols for FILE
	arg.
	Add a note to doc string about the futility of using this on
	dumped lisp.

Signed-off-by: Steve Youngs <steve@sxemacs.org>