SI-7757 disallow constructor annotations on traits

Previously it was possible to define constructor annotations on traits
with really weird side-effects (parser lost the body of the trait). Now
constructor annotations on traits will cause appropriate syntax errors.
SI-7757 add additional test case with annotation on the next line
SI-7756 Uncripple refchecks in case bodies

In 65340ed4ad2e, parts of RefChecks were disabled when
we traversed into the results of the new pattern matcher.
Similar logic existed for the old pattern matcher, but in
that case the Match / CaseDef nodes still existed in the tree.

The new approach was too broad: important checks no longer
scrutinized the body of cases.

This commit turns the checks back on when it finds the remnants
of a case body, which appears as an application to a label def.
SI-6797 Test case for already-fixed DelayedInit bug

Progressed in b4fbb7be0e2, "translation for DelayedInit keeps
more code in original class."
Merge pull request #2839 from densh/topic/si-7757

SI-7757 disallow constructor annotations on traits
Merge pull request #2854 from som-snytt/issue/7729-slash

SI-7729 Fix broken windows build
Merge pull request #2840 from retronym/ticket/7756-2.11

SI-7756 Uncripple refchecks in case bodies
Merge pull request #2853 from retronym/ticket/6797

SI-6797 Test case for already-fixed DelayedInit bug
Par-Test prefers root when seeking build/target
SI-7622 Phase assembly is testable

Fixing hash on nodes makes fault detection deterministic,
which aids testing.

Error messages are shortened and .dot files are dumped
automatically on faults to guard against future flakiness.
SI-7622 -Xgenerate-phase-graph is an info option

-Xgenerate-phase-graph is comparable to -Xshow-phases.

The knowledge about what is an info-only option is refactored
to Settings, which also knows which group of options comprise
the optimiser set.
Repl should early-init its phase global

They're threatening to throw NPE if your SubComponent doesn't
have an early definition of global, so change it now in REPL.

Also, contribute replPhase as an internal phase.
SI-7622 Phases are enabled or not

Refactor the calculation of the "phase chain" a bit.
In particular, initial and terminal phases are not special
except that they must be head and last.

When done, filter for enabled phases. At this commit,
nobody claims to be disabled.

Additional sanity support of phases settings.
SI-7622 -Xshow-phases can show disabled phases

With -Ydebug, -Xshow-phases will show phases that are skipped
or not enabled.

The code is slightly refactored, so the flags table will also benefit.
SI-7622 Plugins can be not enabled

Plugins can interrogate options and declare themselves not
enabled.  The plugin itself can return false from its init
if the options do not compute.  A plugin phase component
can declare itself not enabled, same as an internal phase.

No one exploits this facility at this commit.
SI-7622 Clean Up Phase Assembly

Let optimiser components and continuations plugin opt-out
when required flags are not set.

Wasted time on a whitespace error in check file, so let
--debug dump the processed check file and its diff.