Context escape detection.

During creation of each of DottyTests context is stolen from test and a
WeakReference for it is created.
After running all tests references are examined to detect if any of them
has leaked.
Enable javac lint deprecation&unchecked warnings.
Allow to provide parent Context for Driver.process
Add support for specifying 'all' for -Xprint, -Yskip, etc
Merge pull request #127 from smarter/add/all-phases

Add support for specifying 'all' for -Xprint, -Yskip, etc
Merge pull request #119 from DarkDimius/leaks

Context escape detection.
Constructors stub
CollectEntryPoints.

Collect entry points for backend.
Previously this was done by cleanup.
Helper method to get all members of type.
Fix error in box\unbox logic.

TermRef's for primitive types are of primitive-type.
Fix TailRec to use Label flag.

Conflicts:
	src/dotty/tools/dotc/backend/jvm/BCodeBodyBuilder.scala
	src/dotty/tools/dotc/core/Definitions.scala
Definitions used by backend.
Fix invalid flags in lazy vals.
Better error message if position of tree isn't set.