Minor configuration changes.

[Pavel Roskin <proski gnu org>]

Hello!

Just for your information.

I have just applied several patches that make in easier for the frontends
to coexist peaceflully.

There were some non-trivial definitions in acconfig.h. But acconfig.h is a
wrong place for them, since all "undef" directives will be substituted.
You cannot put there something like

#ifdef HAVE_X
#undef HAVE_SUBSHELL_SUPPORT
#endif

and expect it to work properly. That's why all non-trivial parts of
acconfig.h have been moved to a new file, extraconf.h. It's role is
different from x.h and global.h - it corrects the contents of config.h for
the current edition and defines new symbols based solely on the contents
of config.h, so that configure.in is releaved from implementing this
logic.

Now it's trivial to override the configuration for some editions - you can
compile mc with subshell and gmc without subshell (i.e. without compiling
and linking the subshell code) in the same run.

It is also possible to undefine both HAVE_SLANG and HAS_CURSES in the
GNOME edition. By doing so, I was able to remove some dummy functions from
slint.c. Essentially, the GNOME frontend has been fully untied from the
console graphics libraries. It is now compiled without HAVE_SLANG defined.

-- 
Regards,
Pavel Roskin