SI-6448 Collecting the spoils of PartialFun#runWith

Avoids calling both `isDefinedAt` and `apply`. This pathological
case that would benefit the most looks like:

  xs collect {
    case x if {expensive(); true} => x
  }

The typical change looks like:

-    for (x <- this) if (pf.isDefinedAt(x)) b += pf(x)
+    foreach(pf.runWith(b += _))

Incorporates feedback provided by Pavel Pavlov:

  https://github.com/retronym/scala/commit/ef5430

A few more opportunities for optimization are noted in the
`Pending` section of the enclosed test. `Iterator.collect`
would be nice, but a solution eludes me.

Calling the guard less frequently does change the behaviour
of these functions in an obervable way, but not contravene
the documented semantics. That said, there is an alternative
opinion on the comment of the ticket:

  https://issues.scala-lang.org/browse/SI-6448
comment / question in typers
Optimize primitive Array(e1, ..., en)

Expands an existing optimization for reference arrays to
apply to primitives, as well.

Fixes one aspect of SI-6247.
More principled tree copying.

Canonical > home-spun.
Treat name in getResourceAsStream as resource path

The parameter for getResourceAsStream is not a class name. It's a resource path!
New starr based on 4f98d50bc2 .

Contains the extension method naming change, in the
interests of unbreaking the sbt build for a while.
show developer guidelines on opening pull request

Includes "Improvements and typo fixes to CONTRIBUTING.md" by @heathercmiller
as well as feedback from @retronym.
Remove hostile code from explicitouter.

If that's the $outer accessor, what's that being created
in newOuterAccessor? Sketchy, sketchy business.
Associate correct names to e-mails, correct or not

This is used by git log to produce names with certain formats, and
is used by the release notes tool as well. Helpful if you have commits
with Author not set correctly, as did I.

I'm also including Aleksandar Prokopec and his friend Aleksandar Pokopec,
as well as Pavel Pavlov, both of whom have commits appearing under more
than one name.

I'm not including others who have not set a full name, but don't have
commits appearing under more than one name.
fix t2318.scala
Fix SI-6637 (misoptimization in erasure)

Move the optimization one level deeper so the expression
being tested with isInstanceOf is always evaluated.
Merge pull request #1591 from paulp/new-starr

New starr based on 4f98d50bc2 .
Merge pull request #1595 from paulp/explicit-outer-fix

Remove hostile code from explicitouter.
Hardened JavaMirrors against linkage errors.

After running into a ClassCircularityError and following it
back to this, I simplified the method to route all linkage
errors the same way. And added logging.
Minor tweaks in Types/Scopes.

All methods to do with handling imports more uniformly and early
filtering of symbols which cannot be imported. Also make TypeBounds
treat a Wildcard in lower or upper bounds as an empty bound, so we
don't see all these method signatures like

  def f[T >: ? <: ?]

because that's not helpful.
Massively simplified repl initialization.
Massively simplified repl name resolution.
Moved IMain ops requiring stability into implicit class.

A long-standing annoyance of having IMain stored in a var
is that you can't call a method on it which returns a dependent
type and then pass that to any other method.  I realized I
could get around this by creating an implicit class around
the var; in the class, it is a val, so the method can be written
there, and we implicitly convert from the var on demand.
Cleanups to the previous repl commits.
A utility function to summarize an exception.

Now when I start the repl and trigger an exception during
initialization, it offers a one line message like:

  uncaught exception during compilation:
    AssertionError("assertion failed: (14,13)")
    @ scala.reflect.internal.Symbols$Symbol.updateInfo(Symbols.scala:1309)

Which is a marked debugging improvement from RC1:

  uncaught exception during compilation: java.lang.AssertionError