Make sure 'make' can work after 'make clean'.

Introduce 'distclean' target to remove files generated by configure,
and let 'clean' target only remove files generated by 'make'.

Author: petterreinholdtsen

src/Makefile

@@ -507,7 +507,8 @@ inclean:
 	$(RM) $(INFILES)
 headersclean:
 	$(RM) $(HEADERS)
-clean: docclean pythonclean cscopeclean inclean headersclean
+clean: docclean pythonclean cscopeclean headersclean
+distclean: inclean
 
 # This is the gateway into the crazy world of "kbuild", the linux 2.6 system
 # for building kernel modules.	Other kernel module build styles need to be