ij-legacy (headless): handle radio buttons

GenericDialog gained knowledge about radio buttons in 1.47r.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
ij-legacy (headless): override focus methods

These would potentially access AWT methods that are no longer there
in headless mode.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
ij-legacy (headless): override two more methods

These would potentially cause problems in headless mode.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
ij-legacy (headless): safe-guard against unknown GenericDialog methods

Every once in a while, GenericDialog acquires new functionality that is --
of course -- incompatible with the headless mode. Rather than catch these
problems at the most inconvenient moment, such as in the final stages of a
paper or grant submission, let's catch them when they occur.

To that end, we introduce a unit test whose sole purpose is to figure out
whether there are methods in whatever GenericDialog version we want to use
which the LegacyGenericDialog does not account for yet.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'headless-generic-dialog'

In the wake of the quick-n-dirty fix for GenericDialog's failure to
account for a newly-introduced method that was promptly used by the
File>Import>Image Sequence... command, failing spectacularly in headless
mode, this topic branch tries to make things more robust in the future.

It does so by introducing a unit test detecting newly-introduced methods
(and fixing a few instances that would break the unit test already).

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