Problems due to grep.el introduction

[Eli Zaretskii]

Since the `grep' command and related functions are now on a separate
file grep.el, unbundled Lisp packages that used `grep'-related
features will become broken if they require `compile' and rely on
`grep'-related variables and functions to become defined as a result.
Moreover, the fact that grep.el was added is not even mentioned in
NEWS, AFAICS.

(I bumped into this when I installed ID-utils on a machine with a
relatively recent CVS snapshot of Emacs, and found that "M-x gid"
barfs becaise grep-regex-alist is not defined.)

We definitely should mention grep.el in NEWS, but beyond that, I
wonder whether we should add to compile.el a series of calls to
`autoload' that would cause grep.el to be autoloaded whenever some
program that requires only compile references a `grep'-related
variable or function.  Like this, for example:

   (autoload 'grep-regex-alist "grep")

Comments?