tests: use system hg only if changelog or dirstate can't be read The bundled hg should work flawlessly in most cases. Make it depend on the external installation only if necessary since we can't control the whole environment. This patch doesn't implement the "exit 80" idea proposed by Jun. I don't want to keep the capability checking sync with the actual tests.

tests: restore workaround of obsolete warning from 3c9066ed557c It's simple and works well unless you are using third-party extensions that changes the store format.

tests: alias syshg and syshgenv so they can be switched conditionally

tests: actually restore the original environment before running syshg Since os.environ may be overridden in run-tests.py, several important variables such as PATH weren't restored. I don't like the idea of using the system hg *by default* because the executable and the configs are out of our control. But I don't mind as long as the tests pass.

Added signature for changeset 26c49ed51a69

Added tag 4.2.2 for changeset 26c49ed51a69

phabricator: add phabread command to read patches This patch adds a `phabread` command generating plain-text patches from Phabricator, suitable for `hg import`. It respects `hg:meta` so user and date information might be preserved. And it removes `Summary:` field name which makes the commit message a bit tidier. To support stacked diffs, a `--stack` flag was added to read dependent patches recursively.

phabricator: add phabsend command to send a stack The `phabsend` command is intended to provide `hg email`-like experience - sending a stack, setup dependency information and do not amend existing changesets. It uses differential.createrawdiff and differential.revision.edit Conduit API to create or update a Differential Revision. Local tags like `D123` are written indicating certain changesets were sent to Phabricator. The `phabsend` command will use obsstore and tags information to decide whether to update or create Differential Revisions.