FolderOpener: remember macro options when converting to grayscale

ImageJ 1.x lost the "Convert to 8-bit Grayscale" checkbox without prior
notice some time ago. The ij1-patcher puts it back, but unfortunately
reset the macro options when converting to grayscale.

Reported by Martin ? in http://fiji.sc/bugzilla/show_bug.cgi?id=707

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