Passthrough flags inserted by go test

flag.go

diff --git a/flag.go b/flag.go
index bb03cfc..965df13 100644
--- a/flag.go
+++ b/flag.go
@@ -778,6 +778,9 @@
 }
 
 func (f *FlagSet) parseSingleShortArg(shorthands string, args []string) (outShorts string, outArgs []string, err error) {
+	if strings.HasPrefix(shorthands, "test.") {
+		return
+	}
 	outArgs = args
 	outShorts = shorthands[1:]
 	c := shorthands[0]