simple improvements to make-mode.el

[Robert W Anderson]

In make-mode.el, the definition of makefile-macroassign-regex misses
macro assignments that prepend the keyword "export".  font-lock then
misses them for colorization.

In addition, it seems natural to include in font-lock-keyword-face
additional keywords beyond include directives and conditionals, to
include for example all of GNU make's keywords (foreach, etc.)

What is the proper procedure for submitting these extensions?  diff
against CVS HEAD and mail to the list?

Thanks,
Bob Anderson