[AD] ESD DIGI driver

[Michael Bukin <M.A.Bukin@xxxxxxxxxx>]

http://www.inp.nsk.su/~bukinm/allegro/au012.gz

This patch adds support for DIGI driver working through Enlightened
Sound Daemon.  It does not support playback yet.  It does not work for
me and I can not debug it, because I can not configure esd, so this
driver is disabled by default.  If anyone is willing to try it, then
use `--enable-esddigi' when configuring Allegro.  But if nobody is
going to finish support for esd, then perhaps it should not be
included into the library.

Also, this patch fixes one minor thing.  I did not remove
AC_CHECK_HEADERS(soundcard.h...) from configure.in after adding OSS
DIGI driver.  These headers are tested in aclocal.m4 as part of the
test for OSS support.

-- 
Michael Bukin