fixup! Report the source of a value when we cannot parse it

move bool to the end of the return arguments

remove "from " prefix in the source/fromWhere description

remove TODO notes from functions that don't currently perform error checking

flag_string.go

@@ -57,8 +57,7 @@ func (f *StringFlag) GetValue() string {
 
 // Apply populates the flag given the flag set and environment
 func (f *StringFlag) Apply(set *flag.FlagSet) error {
-	// TODO: how to report source?
-	if val, ok, _ := flagFromEnvOrFile(f.EnvVars, f.FilePath); ok {
+	if val, _, found := flagFromEnvOrFile(f.EnvVars, f.FilePath); found {
 		f.Value = val
 		f.HasBeenSet = true
 	}