Add -epn to check_packages.

Closes: #691012
Thanks: Salvatore Bonaccorso
Fix check_ajp to return CRITICAL on connection errors.
Add config file for check_ajp.
Read 5 bytes only - thats all an AJP pong needs.
Be nice and close the AJP connection socket.
check_ajp: print an error message if --app is not specified.