SI-6807 Deprecating the Actors library.

All public classes, traits and objects marked as deprecated.
Added deprecation note on the package object.
Embedded external libraries (ThreadPool etc.) are not deprecated as they are intended for internal use only.

Review by: @phaller
re-align 2.10.x's pattern matcher with master's

The diff was mostly code cleanup, so most of that was propagated from master to 2.10.x.
The remaining diff is encapsulated in compatibility stubs (see below).
(There was also the on/off potential for the 2.10.x "new" pattern matcher.
 The old one is gone in 2.11, so no turning off new patmat, of course.)

The stubs:

```
protected final def dealiasWiden(tp: Type)   = tp.dealias                       // 2.11: dealiasWiden
protected final def mkTRUE                   = CODE.TRUE_typed                  // 2.11: CODE.TRUE
protected final def mkFALSE                  = CODE.FALSE_typed                 // 2.11: CODE.FALSE
protected final def hasStableSymbol(p: Tree) = p.hasSymbol && p.symbol.isStable // 2.11: p.hasSymbolField && p.symbol.isStable
protected final def devWarning(str: String)  = global.debugwarn(str)            // 2.11: omit
```
[refactor] move PatternMatching.scala to transform.patmat
[refactor] type analysis consolidation

move instanceOfTpImplies out of CodeGen into TypeAnalysis
[refactor] prepare migration from Cond to Prop

There's no change in behavior.
Remove `modelNull` boolean in favor of subclassing.
drop Cond in favor of Prop

This brings the optimizations and the analyses closer together.

In the future we may consider using a solver in the optimizations.
For now, implication is checked ad-hoc using hash-consing and equality/subset tests...

NOTE: prepareNewAnalysis resets said hash-consing, so must be
called before approximating a match to propositions
[refactor] make hash-consing more robust
[refactor] better name for symbolicCase
[refactor] move some logic-related code
Merge branch 'patmat-refactor' into patmat-refactor-master

Conflicts:
	src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
SI-7164 - Removing NotImplementedError as Fatal from s.u.c.NonFatal
Merge pull request #2154 from viktorklang/wip-SI7164-nonfatal-notimplementederror

SI-7164 - Removing NotImplementedError as Fatal from s.u.c.NonFatal
Merge pull request #2082 from vjovanov/deprecate-actors

SI-6807 Deprecating the Actors library.
Merge pull request #2121 from adriaanm/patmat-refactor-master

merge the patmat refactoring into master