chg: fallback to original hg for some unsupported commands or flags There are some known unsupported commands or flags for chg, such as hg serve -d and hg foo --time. This patch detects these situations and transparently fall back to the original hg. So the users won't bother remembering what chg can and cannot do by themselves. The current detection is not 100% accurate since we do not have an equivalent command line parser in C. But it tries not to cause false positives that prevents people from using chg for legit cases. In the future we may want to implement a more accurate "unsupported" check server-side.

testing: add a 'continuous' profile This gives a good way of letting Hypothesis run until it finds an error, save that error, and be restarted without it picking up on the old bug. This lets you run long-running Hypothesis processes and then perform a manual deduplication task on the bugs found at the end. It's not an entirely satisfying way of using this, but anything much better would require extensive changes to Hypothesis itself.

testing: allow Hypothesis to enable extensions This adds support for testing extensions, including both tests that extensions don't change behaviour and test for specific commands. We use the precondition system to determine what commands are available to us. If we never use any commands enabled by an extension then that extension is *skippable* and should not have changed the behaviour of the test. We thus rerun the test with an environment variable which is designed to turn off the extension.

testing: test multiple repositories with Hypothesis This expands the Hypothesis based stateful testing so that rather than having a single repository under test, Hypothesis manages a family of repositories. Some of these are freshly created, some are clones of others.