bad change to tooltip.el

[Nick Roberts]

 > The last change to tooltip.el is bogus -- `case' is no longer
 > expanded.

It appears that three of the features weren't need, so it was 75% right. You
might like to always see the bottle as being half empty, but please remember
some of us prefer to see it as half full.

So that the reason for its inclusion is apparent (I thought it was 
(unnecessarily) there for the cl push and pop macros ), I've added a comment.
Perhaps the suggestion of this practice could replace the current one in
tips.texi.

Of course, once CL has been required for compilation then all the following
lisp files are compiled with those macros, and not those in subr.el which have
been overwritten.

Nick