Merge branch 'jc/optional-path'

Configuration variables that take a pathname as a value (e.g. blame.ignorerevsfile) can be marked as optional by prefixing ":(optoinal)" before its value. * jc/optional-path: parseopt: values of pathname type can be prefixed with :(optional) config: values of pathname type can be prefixed with :(optional) t7500: fix GIT_EDITOR shell snippet t7500: make each piece more independent