Add --nosort

[petdance]

We have to be able to turn off the --sort flag on the command line.

[blmatthews]

When I saw this my first thought was “There’s already a --nosort-files”. It’s mentioned in ack --man, although now that I look closer, just in an example about how ack loads settings. It isn’t mentioned in ack --help, and isn’t recognized as an option (nor is --no-sort-files). However, --sort isn’t mentioned in --help or --man either (but is recognized as an option). Seems like that could all be cleaned up a bit.