fix #24468
fix #20082
fix 'German accent'
add comment
make it C++ and don't translate

translating doesn't work (not this way at least) and won't happen anyway
as the translation mechanism is set up only later in the code, after the
use of the usage() function.
fix formatting
small optimization: call spatium() only once
ignore some backup- and temp. files

for vim and QtCreator
plugin documentation, consistency
plugin documentation

attempt(!) to prevent FileIO to show up twice in the help for plugins
improve mtest

unified diffs are much easier to read and colored in red they stick out
better
break the test

so we have something to see...