cylc run: support "now" as a start tag.
In the test-battery, poll before wait.

This gets the result from each test as it comes in without blocking on
the long-running suites.
test-battery: don't print run dir location.
Two test suites inadvertantly using 'at' scheduler

and would therefore fail if atd was not running.
test-battery: validation failure should be a test failure.
Checked all test suite tasks run as fast as possible.
A simple wait-and-retry loop for the name registration DB.

This only matters if you attempt to register several suites at the same
time, which one test suite now does.
test-battery: only validate the first time through.
Merge branch 'master' into cylc-run.now
Restore sequential sub-suites in tests/events/suite.
Merge pull request #459 from matthewrmshin/cylc-run.now

cylc run: support "now" as a start tag.
Documented 'cylc run now'.
Merge pull request #460 from hjoliver/some-test-battery-improvements

Some test battery improvements
Updated change log for 5.2.0.
New png format view tab icons.
Merge pull request #463 from hjoliver/new-view-tab-icons

New png format view tab icons.
Graph command option to ignore suicide triggers.
Ignore suicide check button for gcylc graph popup.
Ignore suicide option for gcylc graph view.
Updated the change log.