rebase: fix rebase with no common ancestors (issue4446)
The new rebase revset didn't check for the case when there are no common
ancestors. Now it does. The new behavior should be the same as the pre-3.2
behavior. Added a test.
test-run-tests: accept more levels of precision and trailing ws (issue4440)
simplejson produces slightly different output from the built-in json
module, specifically:
* It uses 0.000 instead of 0.0000
* It likes to put a trailing space after a comma
This change works around both of those variations.