Do not minimize APIs if API debugging option is enabled.

That's foundation for API dumping and tests based on API representation contents.

Specific list of changes introduced by this commit:
  * `AnalysisCallback` class takes `IncOptions` as argument so it
    can determine if API should be minimized in `api` callback.
  * Introduce `Incremental.apiDebug` method that determines if api debugging
    is enabled. There are two ways to enable api debugging: through system
    property and through incremental compiler options. The system property
    method will be soon deprecated. We introduce it to make it easier to enable
    API debugging until tools (like zinc and ide) catch up with making incremental
    compiler configurable.

NOTE: The `apiDebug` method has been introduced in Incremental for two reasons:
  1. It's analogous to `incDebug` method that's already there.
  2. In other branch I need `apiDebug` to be defined in Incremental.

Once we deprecate and remove enabling debugging options through system properties
the code will be cleaned up.
Add a pending test-case for showing circular api structures.

This test should pass because `ShowAPI` skips inherited members but
due to sbt/sbt#676 it fails with StackOverflowError.

This makes it a decent test-case for both showing circular api structures
and for the aforementioned bug itself.
Fix sbt/sbt#676: swapped declarations and members in `ClassToAPI`.

As described in sbt/sbt#676, arguments to `mergeMap` and `merge` methods
were swapped causing wrong structures being created for Java compiled
class files.

This commit fixes sbt/sbt#676 and makes pending test to pass now.
Show some of inherited members of a structure in `ShowAPI.scala`

Showing inherited members of a structure was disabled so we would not
run into cycles. To best of my knowledge, we can run into cycles only
if inherited member is `ClassLike`. We filter out those and let
anything else to be shown.
Mark inherited definitions in `ShowAPI`.

Mark every inherited definition with `^inherited^` marker. This helps
understanding `ShowAPI`s output.