bUnwarpJ_ is an external project now

As of e28c018(Add a .gitignore file), bUnwarpJ_ lives in

	https://github.com/fiji/bUnwarpJ

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Ignore if bUnwarpJ_ is cloned into external/

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

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