Let @CFLAGS@ tell us where X include-files are.

Add -lm to -lGL/-lMesaGL tests, to ensure it doesn't fail to find GL
just because libGL/libGLU use sqrt etc.!
Discard tests which search for IrisGL and PEX, since we can't use them anyway.
Re-install "depended"/"Makedepend" fix.  We really do want to force
Makedepend to be rebuilt, I think.

Rather than archiving an (incorrect) copy of Makedepend,
just have "configure" create an empty Makedepend and force
"make depend" to be invoked if the user then says "make".

Now use worldline.h from ${KIRA}/inc directory rather than
the one hidden deep in the source.