SI-7088 Array crasher in erasure.

The usual business where half our pattern matches are missing
half the necessary cases.
Merge pull request #2563 from soc/SI-7474

SI-7474 Parallel collections: End the exception handling madness
SI-7399 : Take scala.concurrent.context.maxThreads into account

This change fixes the bug whereby specifiying maxThread as a property
has no effect. A small refactoring is applied in the process.
Merge pull request #2424 from rjolly/si-7399

SI-7399 : Take scala.concurrent.context.maxThreads into account
Revert "SI-6039 Harden against irrelevant filesystem details"

This reverts commit b0758f5cb9d966b940933d48bdbb45d17a80de66.

This commit sent startup time through the roof, at least
in some circumstances (it is presumably related to one's
current working directory.)
Merge pull request #2614 from paulp/pr/revert-fs

Revert "SI-6039 Harden against irrelevant filesystem details"
Merge pull request #2592 from paulp/issue/7088

SI-7088 Array crasher in erasure.
SI-7479 Make test/files/run/tailcalls.scala pass on Avian

In this commit a new option to the diff fitler is added,
so that the different results of the test on Avian can be
specified in the check file.
SI-7479 Make test/files/run/tailcalls.scala pass on Avian

This commit modifies the test and check file to use the new diff filter.