Introduce Compiler.supportsIncrementalCompilation

[rfscholte]

With this hint the caller can decide which classes should be (re)compiled. In general if incremental compilation is not supported, it is best to recompile everything if something has changed.
(Since Compiler is an interface, this requires Java 8 so a default method can be added)

[rfscholte]

Warning: it is a boolean, but it should have been an integer to define which parts are supported. Don't use the boolean flag! Sadly
the library was released before this could be fixed.

[olamy]

I don;t understand? you pushed that here 7476614
we can change that as not sure it's really used for now and it's a very recent release

[rfscholte]

This was indeed the first approach, but later I discovered that it is not a simple true/false thingy, It must be more finegrained.