Rewrite findBooleanMacroParameter() completely

The new version reads much easier, at least in this developer's
opinion.

Daniel Hornung pointed out a problem with the previous code. This
change fixes it, and other edge cases, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Test more boolean parameter cases

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