Re-enable typechecked types part of quasiquote test suite

It was accidentally disabled.
Merge pull request #3686 from densh/topic/re-enabled-typechecked-types

Re-enable typechecked types part of quasiquote test suite
Bump version for 2.12.x

For this step, we still depend on _2.11 libraries (partest, xml,
parser-combinators).

After we release the first milestone of 2.12, we will update
versions.property to bootstrap to 2.12 dependencies.
Disable MiMa on the 2.12.x branch
Merge pull request #3715 from retronym/topic/bump

Bump version for 2.12.x
Respect -Dpartest.scalac_opts when running the test suite through ANT

Used to enable `-Xcheckinit` (now also `-Ybackend:GenBCode`) when
compiling tests in the respective jenkins builds. This is currently
broken, as you can see in [recent build logs] [1], `-Xcheckinit` is
missing:

    [partest] Scalac options are:  -optimise

Adds `.flags` files for macro tests (correct range positions not
enforced) and for tests failing due to SI-8560 or SI-8562.

[1]: https://scala-webapps.epfl.ch/jenkins/view/nightlies/job/scala-nightly-checkinit/2058/consoleFull