Add AM_MAINTAINER_MODE to configure.in

Add AM_MAINTAINER_MODE to configure.in

Signed-off-by: Kevin Coffman <kwc@citi.umich.edu>
As requested by "Steinar H. Gunderson" <sgunderson@bigfoot.com>, add
AM_MAINTAINER_MODE to configure.in.  See the description of this
macro below:

  `AM_MAINTAINER_MODE' disables the so called "rebuild rules" bys
  default. If you have `AM_MAINTAINER_MODE' in `configure.ac', and
  run `./configure && make', then `make' will *never* attempt to
  rebuild `configure', `Makefile.in's, Lex or Yacc outputs, etc.
  I.e., this disables build rules for files which are usually
  distributed and that users should normally not have to update.

     If you run `./configure --enable-maintainer-mode', then these
     rebuild rules will be active.
Signed-off-by: Neil Brown <neilb@suse.de>