exp/template: simpler parse of char constants.

We can avoid the check against empty constants (''),
which UnquoteChar doesn't handle well, by leaving on
the trailing quote and seeing that's all we have left at the end.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/4657090

src/pkg/exp/template/parse.go

@@ -293,15 +293,12 @@ func newNumber(text string, typ itemType) (*numberNode, os.Error) {
 	n := &numberNode{nodeType: nodeNumber, text: text}
 	switch typ {
 	case itemChar:
-		if len(text) < 3 {
-			return nil, fmt.Errorf("illegal character constant: %s", text)
-		}
-		rune, _, tail, err := strconv.UnquoteChar(text[1:len(text)-1], text[0])
+		rune, _, tail, err := strconv.UnquoteChar(text[1:], text[0])
 		if err != nil {
 			return nil, err
 		}
-		if len(tail) > 0 {
-			return nil, fmt.Errorf("extra bytes in character constant: %s", text)
+		if tail != "'" {
+			return nil, fmt.Errorf("malformed character constant: %s", text)
 		}
 		n.int64 = int64(rune)
 		n.isInt = true