[Bug-gnubg] Autoconf configure changes

[Michael Petch]

Howdy,

I have committed a few changes related to the autoconf configure process
that could affect some people.

AVX has been taken out of the experimental state after a fair amount of
testing and tweaking. The configure process will default to AVX if the
build machine and OS supports AVX.

Previously we were building with g_assert on by default. This behaviour
has changed. The default is off. It can be enabled with this option:

--enable-gasserts       enable g_assert debugging macros (Default disabled)

The default browser for *nix/BSD based builds was changed from Firefox
to xdg-open . xdg-open is a more generic mechanism to open URLs, and is
available across many distributions.

You can override this behaviour with a new --with option:

--with-default-browser=program
                          specify the program to open URLs:
                          (default=xdg-open,
                          or default=sensible-browser on Debian distros)

To get the old behaviour of forcing the browser to be Firefox use:

--with-default-browser=firefox

If you don't specify a program and use it this way:

--with-default-browser

The configure process will look for these ways to launch a browser on
the build machine in this order:

sensible-browser, xdg-open, firefox . If none of these are found it will
default back to xdg-open. If xdg-open isn't available, then launching
the GNUBG manual and the help will not do anything.

-- 
Michael Petch
GNU Backgammon Maintainer / Developer
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