Make the includes be libkmod/libkmod.h for code outside of library. This
fixes the broken build after 1315123 ('build-sys: Don't add libkmod
subdirectory to include path').
It has changed in the past, and these days, anyone can get a copy of the
LGPL via the web rather than by post.
Like 657a122 (Remove FSF mailing address) in libabc by Josh Tripplet,
but let the FSF website in which the license can be found.
Add a modprobe.conf with some blacklist entries in a test rootfs, and
then ensure our blacklist function actually cuts out the two listed
entries (and doesn't cut out the others).