move "CRITICAL" to "PortableXxx", where it belongs and used to be; now that it is no longer used in "Random.sml"

regenerated "metis.ML"

update comment

make "Unprotected concurrency introduces some true randomness." be true; this code is called often and doesn't need to be considered critical. I added CRITICAL by mistake.

fix parsing of higher-order formulas; this code was never exercised before because the current ATPs perform clausification, but someday ATPs might support FOF natively

merged

load code_runtime immediately again