Avoid some warnings from Sun C.

Some versions of Sun C support __attribute__ but don't support the
"unused" or "format" attributes - they don't fail, but they whine a lot.
They also support the "noreturn" attribute, but don't allow it to be
applied to function pointers, only to functions.

Check whether they can be used without warnings, and use them only if
they can.
Merge git://github.com/the-tcpdump-group/tcpdump

Pull changes from the GitHub repository.
Squelch a signed vs. unsigned comparison warning.

(At that point, we've already checked whether rc is < 0, so we know it's
not.)
Some changes didn't make it into 4.4.0.

Fix the CHANGES list by moving some changes that got in after the 4.4.0
release was made into a list for 4.4.1, and add some additional fixes to
that list.