obj-clean.
This basically entails putting ${.CURDIR} in front of the occasional
source file, script, or directory.
Also adds '.include <bsd.obj.mk>' to web.mk so 'make obj' works.
Change gencommercial script to take a '-s' flag pointing to the source
directory, and the portindex script to take an optional additional
parameter indicating the source directory.
Add -D ${.CURDIR} to sgmlformat to follow includes properly.