The AC_PLUGIN() could not properly handle if a plugin is to be enabled
by default. This patch adds support for outputting the correct help
text.
Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Slightly more readable code and fix issue with --enable-$PLUGIN not
biting properly in the generated Makefile.
Signed-off-by: Joachim Nilsson <troglobit@gmail.com>