Add MK_FILE and MK_SQLITE3

- MK_FILE will conditionalize building lib/libmagic and usr.bin/file
- MK_SQLITE3 will conditionalize building lib/libsqlite3, and will disable
  MK_SVN/MK_SVNLITE by proxy
Honor MK_AUDIT, MK_FILE, MK_GPIO, and MK_SQLITE3

lib/libgpio is a standalone library, but it seems logical to conditionalize
it with MK_GPIO
Honor MK_FILE
Install bsm headers if MK_AUDIT != no
Honor MK_AT, MK_FTP, MK_MAIL, and MK_OPENSSH
- Fill in MK_FILE, MK_PMC, MK_SQLITE3, and MK_ZONEINFO
- Fill in etc/pam.d entries per r275291
- Fill in lib/libaudit entries
- Fill in more MK_NTP entries