SI-2796 Warn if early definitions are used with a trait.

For which they (currently) have no special meaning.
GenASM: pipeline disk-write with building of classfiles
GenASM gets a 10% performance boost via switch
Fix SI-5929 - Verify error with finally and pattern match

Don't enter all labels in a method when emitting a forward jump, since some
labels will be duplicated (if defined inside finally blocks). For each forward
jump, enter only the label that is needed for that jump.
Closes SI-5969.

Assumption that we enter tryTwice when inferring
the right alternative with an empty buffer is
wrong.
In this particular bug it manifested itself on
if/then/else which share the same context and 'else'
branch was simply flushing the buffer with an
error from the 'then' branch.
Better explanation for SI-5969.
The comment should now better reflect the joys of tryTwice
as discussed during the code review.
SI-5830 switches: support guards, unreachability

turn switches with guards into guard-free switches by collecting all cases
that are (possibly) guarded by different guards but that switch on the same constant,
and pushing the implied if-then-else into the collapsed case body

```
case C if G1 => B1
case C if Gi => Bi
case C if GN => BN
```

becomes

```
case C => if (G1) B1
     else if (Gi) Bi
     else if (GN) BN
     else default() // not necessary if GN == EmptyTree
```

default() is a jump to the default case; to enable this, we wrap a default() { } labeldef
around the last case's body (the user-defined default or the synthetic case that throws the matcherror)
so we can jump to the default case after the last guard is checked
(assuming unreachability is checked, once we ended up in a non-default case,
one of the guards either matches or we go to the default case)

the unreachability analysis is minimal -- we simply check (after rewriting to guard-free form)
that:
  - there are no duplicate cases
  - the default case comes last

misc notes:
  - can't jump in exception handlers (TODO: a more fine-grained analysis on when we need to jump)
  - work around SI-6015 (test file run/t5830.scala crashed the inliner)
  - propagate type of case body to label def of default case
    (needed for existentials, see e.g., t2683)
  - the default(){} LabelDef breaks SelectiveANFTransform -- workaround: don't write guarded switches in CPS code
    (do the above transformation manually)
SI-6013 Disallow deferred members from intermediate java parents.

76c76b28f allowed for the fact that a Java method can override
a super class method without matching its type in a Scala sense;
it need only match its type after erasure. However that change
went too far, and considered a concrete method in a base class
to override a deferred method in a subclass.
Merge pull request #809 from dragos/issue/fix-5929

Fix SI-5929 - Verify error with finally and pattern match
Merge pull request #814 from hubertp/issue/5969

Closes SI-5969.
Merge pull request #820 from retronym/ticket/6013

SI-6013 Disallow deferred members from intermediate java parents.
tags for AnyVal and AnyRef
Merge pull request #818 from scalamacros/topic/tags-for-anyval-and-anyref

tags for AnyVal and AnyRef
Merge pull request #777 from retronym/ticket/2796

SI-2796 Warn if early definitions are used with a trait.
Merge pull request #803 from magarciaEPFL/offload-classfile-writing-B

performance improvements (10% to 20% depending on HDD vs SSD) in GenASM
Merge pull request #821 from adriaanm/64acb46ab7

SI-5830 switches: support guards, unreachability
Closes SI-5981, SI-5979, SI-5973. Maintenance to Try.
Merge branch 'topic/tryeither-maintenance' of https://github.com/heathermiller/scala into topic/tryeither-maintenance