cli: move search to the new --exclude= naming scheme.

This commit replaces the --no-exclude option with a
--exclude=(true|false|flag) option. The default is to omit the
excluded messages.

The flag option only makes sense if output=summary (as otherwise there
is nowhere to print the flag). In summary output exclude=false and
exclude=flag give almost identical output:
they differ in that with the exclude=flag option the match count
(i.e., the x in [x/n] in the output) is the number of matching
non-excluded messages rather than the number of matching messages.

Note this changes the default for output=summary when no --exclude=
option is given: it used to default to flag and now defaults to true
(i.e. omit excluded messages). This is neccesary to keep the cli
output uncluttered and for speed reasons.