make libfko pointers constant where possible
added test for client --save-packet <file> argument
added --save-args-file and corresponding tests to the fwknop client
Added --save-args-file and --no-save-args text to fwknop man page
minor comment typ fix
added fwknoprc* files
apply const to pf and ipfw firewall function prototypes
minor cleanup to put --enable-all flags in one place
Added strtol_wrapper() libfko utility function for atoi() replacement (#21)

This commit replaces most atoi() calls (which don't report errors) with a strtol()
wrapper function for stronger string -> integer conversion validation.