SI-7502 removing non-existent element from ListMap returns same map.

Current imperative version constructs a new ListMap regardless of
the fact the map doesn't contain the element. Replace it with the
tail-recursive variant that conserves. Also replace some usages with
the invariant now held.
Make all numeric coercions explicit.

Optimistically, this is preparation for a day when we don't
let numeric types drift with the winds. Even without the optimism
it's a good idea. It flushed out an undocumented change in
the math package object relative to the methods being forwarded (a
type is widened from what is returned in java) so I documented
the intentionality of it.

Managing type coercions manually is a bit tedious, no doubt,
but it's not tedious enough to warrant abandoning type safety
just because java did it.
SI-7088 Array crasher in erasure.

The usual business where half our pattern matches are missing
half the necessary cases.
new starr that supports macro ???
less magic in fast track macros

Now that we have a mechanism to declare not implemented macros, let's put
it to good use by reducing the amount of magic applied to fast track.
SI-7461 c.typeCheck(silent = true) now suppresses ambiguous errors

Otherwise use cases like the one shown in the attached test (trying to
typecheck something, which leads to an ambiguous overload error) will
mysteriously fail compilation.
macro engine refactoring

Macro impl bindings now store more information in signatures.
Previously it was a flattened List[Int] corresponding to flattened paramss,
now it's List[List[Int]] to preserve the lengths of parameter lists.
Also now we distinguish between c.Expr parameters and others.

Previously actual and reference macro signatures were represented as
tuples of vparamss, rets, and sometimes tparams. Now they are all
abstracted behind MacroImplSig.

Finally this patch provides better error messages in cases of
argsc <-> paramsc and argc <-> paramc mismatches.
refactors macro tests

putting in a nutshell, this patch:
  * condenses some macro-XXX-a/b/c/... bundles
  * renames some tests to prepare for other macro flavors
  * introduces some additional tests
refactors importers

Introduces better names, factors out recreation of symbols, trees, types
and completes into separate methods, so that they can be overridden in
specialized importers.

The original motivation for this refactoring was to support JIT
compilation of macros, but I think that most of the introduced
improvements to code quality will be useful in trunk.
refactors macro compilation

Upgrades the way that macro defs are compiled by factoring out most of
the logic in typedMacroBody and related errors in ContextErrors into an
standalone cake. This leads to tighter cohesion and better code reuse
as the cake is isolated from the rest of the compiler and is much easier
to evolve than just a method body.

Increased convenience of coding macro compilation allowed me to further
clarify the implementation of the macro engine (e.g. take a look at
Validators.scala) and to easily implement additional features, namely:

1) Parameters and return type of macro implementations can now be plain
c.Tree's instead of previously mandatory c.Expr's. This makes macros more
lightweight as there are a lot of situations when one doesn't need to
splice macro params (the only motivation to use exprs over trees). Also
as we're on the verge of having quasiquotes in trunk, there soon will be
no reason to use exprs at all, since quasiquotes can splice everything.

2) Macro implementations can now be defined in bundles, standalone cakes
built around a macro context: http://docs.scala-lang.org/overviews/macros/bundles.html.
This further reduces boilerplate by simplifying implementations complex
macros due to the fact that macro programmers no longer need to play
path-dependent games to use helpers.
refactors macro runtimes

Following typedMacroBody, macroRuntime along with its friends has also
been moved out into a separate component.
changes some definitions to use Symbol.map
applying Jason's aesthetics suggestion
Merge pull request #2593 from paulp/pr/no-numeric-widen

Make all numeric coercions explicit.
SI-7474 Parallel collections: End the exception handling madness

"What's wrong with an API which non-deterministically returns either
type A or type B(Set(A, ...))?"

This is pretty much what the exception handling behavior of the
parallel collections does: If exceptions of type A occur, either an
exception of type A or an exception of type B, wrapping multiple
exceptions of A's, is returned.

This behavior is incredibly broken and so unintuitive, that even
people writing tests don't handle it correctly, as seen in test
files/run/t5375.scala.

Concerning “non-deterministic”:
How many exceptions are observed before the operation is aborted
depends on the machine, the available cores and hyper-threading,
the operating system, the threadpool implementation and
configuration, the size of the collection and the runtime itself.

In fact, files/run/t5375.scala can be made to fail reproducible
on both jdk7u and Avian, if we run on a single-core machine
like in a virtual machine.

With this change, we just pass the "first" exception which occurs.

This is
- consistent with the behaviour of sequential collections,
- doesn't require users to know more about parallel collections
than they already do ("elements might be processed out of order"),
- in line with what Java 8 does.

“Why don't we wrap everything in CompositeThrowables?”
Even consistently returning CompositeThrowable doesn't make much
sense (because we have fail-fast behaviour and don't wait until
all tasks have finished or have thrown an exception).
Therefore, there is no useful semantic in having a
CompositeThrowable which returns "some" exceptions.

I have done extensive research into C#'s approach (which is very
similar to what Scala did until now, but even more messy) and
the key observation from asking multiple C# developers is that
not a single one had understood how PLINQ handled exceptions or
could describe the semantics of it.

As a consequence, either
a) gather and return all exceptions in a CompositeThrowable or
b) just return one, unwrapped,
instead of non-deterministically wrapping a non-deterministic
number of exceptions into a completely unrelated wrapper type.

Considering that changing the parallel collection semantics in
such a profound way as described in a) is out of question, b)
is chosen.

As soon as Scala targets Java > 7 Throwable#addSurpressed can be
used to add further exceptions to the one which gets returned.
This would allow passing more information to the caller without
compromising the simplicity of the API.
Merge pull request #2579 from vigdorchik/list_map

SI-7502 removing non-existent element from ListMap leaves it unchaged.
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
SI-6309 Test case for early-init / private[this] crasher.

This has worked since 98daf03, "Overhauled local/getter/setter name logic.".