bin/ack-wrapper: Correctly escape user-supplied args

When using "ack needle foo*.txt", the shell will expand that
wildcard and if any of the matching files contain spaces (or other
special chars that need escaping) those won't be passed correctly
to 'ack' when using the old-style "command ack $ackrc $*" calling
method. We need to single-quote wrap any arguments to ensure we
don't need to escape-out any spaces/exclamation/question chars.
.ackrc: Always print filename, search *.txt files