btrfs-progs: use autotools for building

Since we're building shared libraries now, let's not reinvent the wheel.
This also makes packaging libbtrfs much easier.

(Fixes to make this patch work with upstream by Mark Fasheh)

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.de>