Compile avoidance should respect public constant changes

[oehme]

The API extractor used by the new @CompileClasspath snapshotter drops public constants, making incremental builds incorrect. This affects the following use case:

class A {
  public static final int FOO = 1;
}

class B {
  public void bar() {
    System.out.println(A.FOO);
  }
}

When A.Foo is changed, B should be recompiled, but isn't, resulting in wrong results.

[melix]

To be clear, this happens independently of incremental compilation and only if the 2 classes are in different projects.

[oehme]

The only workarounds are calling clean or --rerun-tasks or making a dummy change to B.

[melix]

Here's the tentative fix. It coincidentally fixes #1474 when used with JDK 8 (but not JDK 7).

[oehme]

Fix looks good to me.