sb-grovel & sb-posix symbol export changes
... sb-grovel no longer quietly exports every constant
... instead, I restored the old default of not exporting the symbol
(and, additionally:) unless asked to
... sb-posix now exports all groveled-for constants and
... (implicitly:) sb-bsd-sockets now does no more export its
constants. This corresponds to the behavior before 0.8.11.65.