Fix problems preventing the system building in non-C grades.

compiler/mode_info.m:
	Avoid a warning due to he Mercury clause for the predicate
	old_and_new_may_differ/2 having too tight a determinism.

compiler/pickle.m:
	Fix cut-and-paste errors in Erlang foreign procs.

deep_profiler/DEEP_FLAGS.in:
	Specify the location of the Erlang library headers.