Convert inet-related functions to new fmgr style. I have also taken it

Convert inet-related functions to new fmgr style.  I have also taken it
on myself to do something about the non-self-consistency of the inet
comparison functions.  The results are probably still semantically wrong
(inet and cidr should have different comparison semantics, I think)
but at least the boolean operators now agree with each other and with
the sort order of indexes on inet/cidr.