Systematically test the exclude options for search. Also move the
search existing exclude tests into the new test. There is some overlap
between the two sets of tests but many of the existing ones are there
because they triggered bugs in the past so I have kept them to ensure
coverage.
Move the option --no-exclude to the --exclude= scheme. Since there is
no way to flag messages only true and false are implemented. Note
that, for consistency with other commands, this is implemented as a
keyword option rather than a boolean option.
The tests for the exclude code in search and count use the line
notmuch config set search.exclude_tags = deleted
which actually sets the exclude tags to be "=" and "deleted". Remove
the "=" from this line.
