Re: gdb-ui.el assumes images support

[Nick Roberts]

 >     If this is the case, tooltip does not need the last three requires,
 > 
 > Please try deleting them and see what happens.

I've done this, followed by "make bootstrap". Since I can find no problem,
I've committed this change. I think there are many other files with requires
that, similarly, aren't really needed. Possibly because of what Luc has
pointed out it says in the manual:

> Sometimes adding a `require' for another package is useful to
> avoid compilation warnings for variables and functions defined in
> that package.  If you do this, often it is better if the
> `require' acts only at compile time...

I've also deleted the require for cl. Using this at compile time, presumably
compiles in expansions of the Common Lisp macros for push and pop, rather than
those in subr.el, which might be undesirable.

Nick