Verify that default values are *not* put into the index

This is a subtle issue: if an annotation for a given class does not
specify a particular value, the developer obviously intended the default
value to be used. Now, if the default value ever changes, it should be
reflected in the values returned by the annotation index. That implies
that we must not write out unspecified settings into the serialized
annotations, but always infer them at runtime from the annotation class
itself.

Happily, our annotation processor does The Right Thing (but the
EclipseHelper in its current form does not). Keep it that way.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Test that EclipseHelper does not serialize default values

The switch to reading annotations directly from .class files in the
EclipseHelper fixed a subtle bug: default values for annotation
parameters must not be serialized into the annotation index, but instead
be inferred at runtime (in case the default values in the annotation
class itself changed).

Keep this bug fixed by testing for it in the unit tests.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>