[AD] Patches applied from my pthreads branch

[George Foot <gfoot@xxxxxxxxxx>]

I've merged the pthreads branch back into the main branch, in my
working copy, and looked at the differences.  I've applied a few
patches which I seem to have made on the wrong branch by
accident:

    * Changes to the program linking options
        The programs were pulling in loads of libraries they
        didn't need -- all of Allegro's dependencies were being
        linked even though they're not required in the shared
        library version.  I've patched the configure script and 
        misc/deplexe.sh to only link these libraries when the
        programs are static.

    * The configure script now tests for pthread support
        This is mostly a side-effect of the above patch, but it
        should be totally harmless.  This affects configure.in
        and include/allegro/alunixac.h.

    * xsystem.c and lsystem.c no longer attempt to hook SIGKILL
        AFAIK it's impossible to hook SIGKILL, that's the whole
        point of SIGKILL vs SIGTERM.  Or is there an OS that
        lets you do this?

The remaining changes are only the pthread background routine
ones, which I'll consolidate and post a patch for.

George

-- 
Random project update:
06/03/2001: AllegroGL 0.0.10 released at http://allegrogl.sourceforge.net/
	Six months' worth of changes, including Mingw32 support!