[PATCH 1/3] Some patches for 2.6.15

The following compiler option was added in kernel version 2.6.15:

   -include include/linux/autoconf.h

That's fine when building drivers using the kernel kbuild system as 
everything is built from the top-level kernel source directory in that 
case.  However, Comedi doesn't do that, so the above compiler option 
causes errors.

The attached patch effectively rewrites the compiler option to:

   -include $(LINUX_DIR)/include/linux/autoconf.h

where $(LINUX_DIR) is the configured kernel source directory (it is 
called $(LINUXDIR) in m4/as-linux.m4).

The patch changes m4/as-linux.m4, which originally came from the 
"autostars" project on sourceforge, so maybe it needs fixing upstream.