Merge branch 'dk/parseopt-optional-filename-fixes'

A recently added configuration variable and command line option syntax ":(optional)" for values that are of filename type inconsistently behaved on an empty file (configuration took it happily, while the command line option pretended as if it did not exist), which has been corrected. * dk/parseopt-optional-filename-fixes: parseopt: remove unreachable code parseopt: restore const qualifier to parsed filename config: use boolean type for a simple flag parseopt: use boolean type for a simple flag doc: clarify command equivalence comment parseopt: fix :(optional) at command line to only ignore missing files