Tidy up bridge_input

No functional change.
Sort options. Use Ss for non-standard headers. New sentence, new line.
Add missing Op.
Sync usage with manpage.
Restructure bridge_input and bridge_broadcast

There are two changes:
- Assemble the places calling pktq_enqueue (bridge_forward)
  for unicast and {b,m}cast frames into one
- Receive {b,m}cast frames in bridge_broadcast, not in
  bridge_input

The changes make the code clear and readable. bridge_input
now doesn't need to take care of {b,m}cast frames;
bridge_forward and bridge_broadcast have the responsibility.

The changes are based on a patch of Lloyd Parkes submitted
in PR 48104, but don't fix its issue yet.
accomodate FreeBSD's flavor of weak references.
fix second line of synopsis.
Fix usage. The man page is incorrect with respect to -I and -i and need
fixing, but my troff foo is not there.
Suppress space after -I and -i options.
Suppress space after -I and -i options in description too.
XXX: This should be documented explicitly.
add mkostemp, mkostemps, mkstemps from FreeBSD.
add mkostemp{s,} mkstemps from FreeBSD
bump libc.
more man pages links
more mktemp flavors.
Don't depend on weak aliases to define the vi "alias" expansion function,
provide an API instead to set it.
Adjust to the new alias text libedit API.
Add stdlib.h for abort() (Jess Thrysoee)
Revert last change. This is not the right place for rumpuser_sync_icache().
cast gotsig because it is long on some systems.
Fix "shadows a global declaration" compile error.