configure: Removed deprecated lines for unused X stuff
configure: Enable compiler warnings for trampoline code generation

This attribute reports cases where GCC has to generate special code to
handle some C constructs, for which we'd prefer an explicit code instead
of counting on GCC doing the work.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
configure: Replaced deprecated construct with recommended new check

The macro 'AC_ISC_POSIX' is now said to be deprecated, so we use the new
recommended check instead as we make light use of the corresponding
function.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
configure: Removed macro that are not used anymore

...and took opportunity to add the traditional copyright notice

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
configure: Added m4 check to detect possible non-expanded macros

When autoconf encounters a macro name that it does not know, it assumes
that it is just a standard keyword that needs to end up in the generated
configure script.

This patch teaches m4 about the syntax used for our macros so it can now
that it is supposed to be a macro, and then it can stop and report the
problem.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WINGs: Removed unnecessary type conversion

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WRaster: Removed unused variables from Makefile

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
wmaker: Do not create a temporary variable for Xrandr support detection

The other extension detection have the same situation and they already
have a variable for that, do not do differently for Xrandr because it adds
unnecessary complexity in the code.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WPrefs: Add case check to fix -Wmaybe-uninitialized warning

The default case should not arise because the tested variable is an enum,
but it the case someone would get a value wrong, we're safer with a little
warning and proper fallback than with unknown behaviour.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>