ignore Cabal sandbox directories by default

Cabal sandboxes are sandbox environments for Haskell packages,
containing compiled packages and a bunch of metadata that users of
ack are unlikely to want to search.  Therefore ignore .cabal-sandbox
directories by default.
added rst
Why is this localized?
no need for L<>
Fixed quotes
Quiet some policies
Simplify to_string() and make it deterministic
Add explicit returns
Quiet more warnings
removed unnecessary block
Add explicit return
rename some vars
Remove unnecessary diag
fixed indents
Prefer qw()
Add new first_line_like() function
Return config hash from _remove_redundancies on Windows
combine some tests into a test_deeply
use File::Next instead of File::Find
Test suite runs under taint flag