SI-2038 make pt fully-defined when typing Typed

dropExistential turns existentials in the expected type (pt) that's passed to `typed`
into `BoundedWildcardType`s, but those should not end up in trees

when typing a `Typed` node, we didn't check for the type being fully defined (`isFullyDefined`)
(and thus did not make it fully defined by turning these BWTs into existentials again using `makeFullyDefined`)
Avoids loading scala.package and scala.reflect.package from source if a classfile exists.

We know that loading these packages from source leads to compilation errors. To reproduce: Update scala.reflect.package, make sure it is on the source path and recompile anything using it. You will get a number of errors having to do with ClassTags and macro expansions. With the patch, these errors go away because the package is not loaded as long as a classfile exists.
New Executor.

To try it out:

run "instrument worksheet" as usual in the REPL. Worksheet needs to have enclosing object definition. Say it is named "Obj".

This will generate a file Obj$instrumented. You can compile that file separately and run it using Java. It should reproduce itself.
Disable interrupts during code instrumentation

Code instrumentation needs to see a consistent snapshot of a source file. To achieve that we disable interrupts during getInstrumented.
Adds method askForResponse

Adds method askForResponse which returns a response immediately instead of waiting for a result. That way, one can wait for an ask's result using a timeout.
Raw string interpolator

Adds a raw string interpolator raw"..." which does not do any escape sequence processing.
New Worksheet mixing scheme

Debug changes
Closes SI-5882

I have added a restriction that value classes may not contain inner classes or objects. This makes sense as the "outer" field of any such classes or objects would be ephemeral, with surprising results. SIP-15 has been changed accordingly.
Closes SI-5878

We need to impose an additional rule on value classes: They may not unbox directly or indirectly to themselves.
SI-5799 Secondary constructors in value classes not allowed

I changed the SIP and added a test.
Fixed SI-5603. Early definitions now get transparent positions.
This includes a fix for a minor problem described in #594 -
ensureNonOverlapping still focuses on default position when outside of early defs.
Review by @dragos, @odersky.
Fixed SI-5031. Only consider classes when looking for companion class.
sym.effectiveOwner revealed this piece of inconsistency. companionModule
is fine because similar check is there already.

Review by @paulp.
ClassTag.Nothing now throws an exception

Nothing is a bottom type, so it doesn't make much sense for it to have
a meaningful erasure (ClassTag.Nothing.runtimeClass).
SI-5866 Support casting null to value classes

The fix now supports null.asInstanceOf[C] where C is a value class that wraps a primitive type.
Merge pull request #1005 from odersky/topic/worksheet

IDE improvements, with particular focus on making worksheets work.
Merge pull request #1013 from odersky/ticket/5878

Closes SI-5878
Merge pull request #998 from odersky/topic/bootpackages

Avoids loading scala.package and scala.reflect.package from source if a ...
Removed resolveOverloaded

It was decided to remove it until the next release
Merge pull request #1015 from hubertp/2.10.x-issue/5603

Fixed SI-5603. Early definitions now get transparent positions.
Merge pull request #960 from clhodapp/remove-resolve-overloaded

Remove resolveOverloaded