fix SI-5829: refinement typeref has a prefix
Cleaning up some code introduced for the old presentation compiler long time ago. Review by @dragos
Closes SI-5821.

This was an interesting one. Basically an erroneous
import was creating an erroneous symbol for Array (similary
for other symbols that were 'found' in this import) which was
leading to all sorts of inconsistencies and spurious errors.

This wasn't a bug in ContextErrors but rather something that
existed for ages and was hidden from the general audience.

Review by @paulp.
Fixes SI-5085 and SI-4833.
don't error when not emitting required switch

we don't handle switches with guards, whereas the old patmat did
to ease the transition, let's not error out and see how we can resolve this
Merge pull request #623 from adriaanm/ticket/switch-warning-not-error

don't error when not emitting required switch
Merge pull request #621 from axel22/issue/5085b

Fixes SI-5085 and SI-4833.
Merge pull request #613 from hubertp/issue/5821

Closes SI-5821.
Merge pull request #624 from hubertp/topic/cleanup

Cleaning up some code introduced for the old presentation compiler long ...
SI-5318 Make implicit divergence checking PolyType aware.

Replaces the two active subclasses of `SymCollector` with
direct use of traversal methods of `Type`.

Wildcard free class type parameters, not just method type parameters,
when stripping the core type of candidate implicits. The spec doesn't
make any such distinction, and the enclosed test, t5318c, crashes
without this change.
Test case closes SI-4818

Fixed between 2.10.0 M2 and M3, with both the old and new pattern matcher.
Merge pull request #625 from retronym/ticket/5318-3

SI-5318 Make implicit divergence checking PolyType aware.
Test case closes SI-4911.

The unchecked warning departed sometime between 4afae5be...278a225.
Test case closes SI-5041.
Merge pull request #629 from retronym/ticket/4911

Test case closes SI-4911.
Merge pull request #630 from retronym/ticket/5041

Test case closes SI-5041.
Merge pull request #626 from retronym/ticket/4818

Test case closes SI-4818
Merge pull request #612 from adriaanm/ticket/5829

fix SI-5829: refinement typeref has a prefix
Help our new exhaustiveness checker.

...be a little less chatty.
Orphan checkfile remover.

Are these -msil checkfiles used in some secret fashion? The level of
activity suggest otherwise.  Since scala-nightly-msil has been disabled
for over a year, it's an easy rm unless someone speaks up.

  % tools/rm-orphan-checkfiles
  Scanning for orphan check files...
  rm 'test/disabled/run/code.check'
  rm 'test/files/jvm/t1652.check'
  rm 'test/files/neg/macro-argtype-mismatch.check'
  rm 'test/files/neg/macro-noncompilertree.check'
  rm 'test/files/neg/macro-nontree.check'
  rm 'test/files/run/Course-2002-01-msil.check'
  rm 'test/files/run/Course-2002-02-msil.check'
  rm 'test/files/run/Course-2002-03-msil.check'
  rm 'test/files/run/Course-2002-04-msil.check'
  rm 'test/files/run/Course-2002-08-msil.check'
  rm 'test/files/run/Course-2002-09-msil.check'
  rm 'test/files/run/Course-2002-10-msil.check'
  rm 'test/files/run/absoverride-msil.check'
  rm 'test/files/run/bitsets-msil.check'
  rm 'test/files/run/boolord-msil.check'
  rm 'test/files/run/bugs-msil.check'
  rm 'test/files/run/impconvtimes-msil.check'
  rm 'test/files/run/infix-msil.check'
  rm 'test/files/run/iq-msil.check'
  rm 'test/files/run/macro-invalidret-doesnt-conform-to-impl-rettype.check'
  rm 'test/files/run/macro-rettype-mismatch.check'
  rm 'test/files/run/misc-msil.check'
  rm 'test/files/run/promotion-msil.check'
  rm 'test/files/run/richs-msil.check'
  rm 'test/files/run/runtime-msil.check'
  rm 'test/files/run/tuples-msil.check'
  rm 'test/pending/jvm/t1464.check'
  rm 'test/pending/run/subarray.check'
  rm 'test/pending/run/t0446.check'
  rm 'test/pending/run/t5629.check'
  Scanning for orphan flags files...
  rm 'test/files/neg/macro-argtype-mismatch.flags'
  rm 'test/files/neg/macro-noncompilertree.flags'
  rm 'test/files/neg/macro-nontree.flags'
  rm 'test/files/pos/anyval-children.flags'
  rm 'test/files/pos/t3097.flags'
  rm 'test/files/run/macro-invalidret-doesnt-conform-to-impl-rettype.flags'
  rm 'test/files/run/macro-rettype-mismatch.flags'