SI-6725 `f` interpolator now supports %n tokens

Currently the `f` interpolator supports format specifiers which
specify conversions for formatted arguments. However Java formatting
is not limited to argument-related conversions as explained in:
http://docs.oracle.com/javase/6/docs/api/java/util/Formatter.html#detail.

Conversions which don't correspond to any arguments are `%` (used to
emit verbatim `'%'` characters) and `n` (used to emit platform-specific
line separators). Of those only the former is supported, and this patch
fixes the oversight.
SI-7132 - don't discard Unit type in interpreter
SI-7233 Account for aliased imports in eta expansion.

Buggy:

    treeCopy.Select(sel, sel.qual, sel.name) setSymbol null
    Select(sel, sel.qual, sel.name)

Okay:

    treeCopy.Select(sel, sel.qual, sel.name)
    Select(sel, sel.qual, sel.symbol.name) // but doesn't copyAttrs!

It is an easy mistake to make, I've found one more occurance:

  def foo(a: Any) = { import a.{toString => toS}; toS }

    error: uncaught exception during compilation: scala.reflect.internal.FatalError
    scala.reflect.internal.FatalError: class Object does not have a member toS
        at scala.reflect.internal.Definitions$DefinitionsClass.scala$reflect$internal$Definitions$DefinitionsClass$$fatalMissingSymbol(Definitions.scala:1028)

A followup commit will address that problem.
SI-7233 Account for aliased imports in Erasure

When we discard the fiction of `scala.Any`.
SI-5513: add inplace set-theoretic operations for mutable bitsets.
SI-7240 fixes language feature lookup

As I discovered today, Definitions.getMember have a fallback clause,
which accounts for the phases which have inner classes flattened.

This fallback uses nme.flattenedName to compute a flattened name, but
unfortunately nme.flattenedName produces a TermName, not a TypeName,
which means that the fallback will commence search in a wrong namespace
with predictable results.

The commit also changes another usage of nme.flattenedName in a type name
context. That one was correctly converting a TermName result to TypeName,
so this is not a bugfix, but just a refactoring for the sake of being
consistent.
Warn about forgotten string interpolators.

In the compiler sources this arrives with a number of false
positives, because we frequently work with strings containing
$foo where foo is an in-scope identifier. I think in normal
source code this will be less of a problem, or none at all;
but to be conservative the warning is born under -Xlint.
Eliminate a bunch of -Xlint warnings.

Mostly unused private code, unused imports, and points where
an extra pair of parentheses is necessary for scalac to have
confidence in our intentions.
Removed dead src directory.

One line of commentary referenced from nowhere can't be very useful.
Merge pull request #2227 from mergeconflict/2.10.x-SI-7132

SI-7132 - don't discard Unit type in interpreter
Merge pull request #2222 from scalamacros/ticket/6725

SI-6725 `f` interpolator now supports %n tokens
Merge pull request #2230 from retronym/ticket/7233

SI-7233 Account for aliased imports in EtaExpansion / Erasure
Merge pull request #2234 from scalamacros/ticket/7240

SI-7240 fixes language feature lookup
Optimize rebalance method by using null optimized list implementation.

rebalance method relies heavily on s.c.i.List. By replacing List with null
optimized version, NList, rebalance operation is significantly more faster.
Test indicate +10 % performance improvement for tree sizes >= 100.

Existing tests verify red-black tree invariants, including operations
involving tree rebalance.
SI-7236 Deprecate ThreadPoolTaskSupport and friends
Removed -Ynotnull setting.

It never worked and it would periodically jump out and bite
someone. Slash and burn so new plants can take root. Eliminated
NotNullType and NotNullClass, internal elements. Removed notNull
method on Type, which no longer has a purpose. Retained 'def
isNotNull' because there are types which are known by construction
not to be null (ThisType, ConstantType as long as the constant
isn't null, etc.) and that's still useful to know.
Remove -Xcheck-null setting.

Maybe this was useful in some way; but no way I ever saw.
I have comments which tell me this is exposed in the IDE so
I left a stub.

I also removed mkCheckInit. That probably sounds like it's related
to -Xcheckinit. Guess again, guy-who-thinks-names-mean-things. It
was only used by -Xcheck-null.
SI-7247, deprecated NotNull.

Removed NotNull from tests and the parentage of AnyVal.

Removed the tests which were actually testing anything to
do with NotNull; massaged the others to forget NotNull and/or
not to name local things NotNull.
Completely remove isNotNull/notNull.

Restarted the Zamboni and collected these as well.
Author was convinced by reviewer that clinging to
isNotNull like Linus's security blanket will not
help us with landing a picture of the Great Pumpkin.
YAGNI, Charlie Brown.
Eliminated containsNull.

This was a little trickier than the previous. I introduced
a new method 'isBottomSubClass' which is the obvious complement
to the beloved 'isNonBottomSubClass'. In eliminating the two
call sites of containsNull I might have overshot the mark a
bit when I rewrote fourthTry and thirdTryRef, but who is going
to argue with such beauty as this.