autoconf orthogonality

It helps automated builds to be able to specify both --with and --without,
--enable and --disable.  This patch begins some of that for bulk_extractor's
autoconf.
It or an analog to set 1 || 0 based on $enableval is needed if USE_LIGHTGREP is used within your code.  I didn't audit the code for use of the options, just made changes so that the knobs would turn off and on properly.