merge with stable

verify: improve progress descriptions For GUIs, the progress bar is disconnected visually from the text that is output by ui.write(), so it's better to be a little bit redundant in naming the status. "checking" is redundant, since the user is running the verify command. 'changesets', 'manifests', etc, tell the user what is being checked (the entity being counted in the progress bar.

pylint, pyflakes: remove unused or duplicate imports

Fix --blacklist when --jobs > 1 in run_tests.py. The options parsing logic replaces the options.blacklist initial value, a list of filenames, with a dict of test names to filenames. When runchildren rebuilds the command line to launch child processes the dict is flattened and provided as a malformed argument when a filename is expected. Fix is to remove the blacklist option from child invocations since the filtering is handled in the parent anyway.

merge with stable

run-tests.py: reset env variables set by hooks