Remove implicit conjunction

I thought that since "tcp port 80" should parse as "tcp and port 80" that in fact the implicit "and" that the pflang spec mentions as obsolete was in fact current.  This faulty conclusion was based on my bad understanding of how "tcp port 80" parses -- that in fact as issue #15 indicates, "tcp port 80" is one operator.

So, we should remove the implicit conjunctions from the parser.
this is an incorrect change because it will leave prec as nil.  dunno what the right fix is; you might try to identify the patch that introduced this behavior and see how to revert it.