again, the convenience functions flag() and noflag() have been used and
all occurrences of 0 and 1 are replaces by true and false. This makes it
safe (and more readable!) to test for active/inactive flags.

Also specify $FLAGS_PARENT explicitly, to avoid having the generated usage
texts by shFlags mention the full Unix path to $0, but instead use the
more recognizable varient 'git flow feature'.