Fix adding manpages installed by LOCAL_DIRS to whatis file.

The ordering of 'etc' in the install has a long history dating back to the
first time it was realized it needed to be "last" in r4486. That commit
still left it before LOCAL_DIRS though. By having it before LOCAL_DIRS
any manpages they install were not being added to the whatis database in the
install image. They would likely show up in the file after a periodic
rebuild of the file though.

Currently the whatis file is built by an 'afterinstall' hook in etc/Makefile
that calls share/man's 'makedb' target.

MFC after: 2 weeks
Sponsored by: EMC / Isilon Storage Division