Update rc.d-unicorn script

Use $rc_pid properly in unicorn_reload() and unicorn_reopen_logs().

Included is a patch which fixes issues with _find_processes not
detecting “ruby19: unicorn” as the correct process entry. This issue is
currently referenced in FreeBSD PR conf/169047 from 2012 but has not
yet been closed. An updated patch has been provided to the bug-followup
address.