… from 3.6 to 3.5 (#2540)

* [3.6] bpo-29512, bpo-30776: Backport regrtest enhancements from master to 3.6 (#2513)

* bpo-29512: Add test.bisect, bisect failing tests (#2452)

Add a new "python3 -m test.bisect" tool to bisect failing tests.

It can be used to find which test method(s) leak references, leak
files, etc.
(cherry picked from commit 84d9d14)

* bpo-30776: regrtest: reduce memleak false positive (#2484)

Only report a leak if each run leaks at least one memory block.
(cherry picked from commit beeca6e)

(cherry picked from commit a3ca94d)

* bpo-30764: Fix regrtest --fail-env-changed --forever (#2536) (#2539)

--forever now stops if a fail changes the environment.
(cherry picked from commit 5e87592)
(cherry picked from commit 4132adb)

…o 2.7 (#2541)

* bpo-29512, bpo-30764: Backport regrtest enhancements from 3.5 to 2.7

* bpo-29512: Add test.bisect, bisect failing tests (#2452)

Add a new "python3 -m test.bisect" tool to bisect failing tests.

It can be used to find which test method(s) leak references, leak
files, etc.

* bpo-30764: Fix regrtest --fail-env-changed --forever (#2536) (#2539)

--forever now stops if a fail changes the environment.

* Fix test_bisect: use absolute import