Rename all the test output files to tree rather than pick, move the
containing directory to a tree.expected-output and fix up the
references in the test.
This changes all the lisp names from pick to tree (variables,
functions etc). It also changes the lisp in the emacs-pick test files
to match the new names.
Currently we support both string and list forms of tag-changes for
historical reasons. This is about to change, so fix pick's tests that
use the legacy string form of tag-changes.
The test should be run using the wrapper run-tests.sh. This links
the tests into the normal notmuch TEST_DIRECTORY and runs them from
there. After the test is complete then the links are removed.
