Make --with-nethack a non-default option.
Use deprecated AC_HAVE_LIBRARY to find mingw opengl32 library
because AC_HAVE_LIB fails -- we need a prototype for even
zero-argument functions like glEnd.

check for libfltk_gl.a and .so.  Can't (?) use AC_CHECK_LIB
since it only has C++ entry points.

  --with-{elumens,ieeeio}{,-lib,-inc}
  --with-model  (for Maya models)
Always enable USE_NETHACK and USE_WARP for now.

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".

Lots of changes to support new time flow and additional
time-related GUI.  Probably not all there but at least somewhat usable.