Limit what options may go into an ackrc file

[petdance]

The way that ack treats the ackrc file like just another source of command line arguments is dangerous. There's no legit reason for someone to put, say, -f or -g or --match or --output or -c or -x in their ackrc file.

The list of options that seem sensible to me are: -i, -S, --column, -s, --pager, --heading, --break, --group, --proximate, --underline, --color*, --flush, --sort-files, --ignore*, -r, -n, --follow, --type-add, --type-set, --type, -k, -A, -B, -C.

Basically anything that regulates behavior vs. regulating output should be forbidden.

[petdance]

This is related to #57. The way we decide what options are mutex is tied to groups of options and their meaning.

[petdance]

Certain options are "actions", for lack of a better word. These can only be on the command line.

-v
-Q
--lines
--match
-l
-L
-o
--output
--passthru
-c
-f
-g
-print0 (only works with other actions)
--show-types
--files-from
-x
--help-types
--version
--ackrc
--create-ackrc
--dump
--help
--man
--faq
--cookbook
--thpppt
--bar
--cathy

[n1vux]

Makes sense. And not really much extra work since we're already filtering a few for security.

[n1vux]

(Although putting --cathy or --thpppt in a project .ackrc would be an amusing prank.)