don't try to handle -include in two places
handle -include-pch

This was already kind of handled by not knowing the option, but this
way it doesn't complain in debug about the "two" source files.
prevent ICECC=no from serializing too much

Because of the file-based locking, ICECC=no always serialized to run
one by one, even on SMP systems. Make it serialize only by the max number
of jobs, using the daemon. Add ICECC=disable to avoid contacting the daemon
completely (=the old ICECC=no).
update the text of the GPL (not the version)

This merely updates the license text to the latest GPLv2 text (fixing
the FSF address). This does not do any actual license change.
make sure to not hide e.g. SEGV from a tool with exit code 0

In particular, 'icerun <foo>' should not exit with 0 if foo segfaulted.