partial correction for CL 1983043: fix various godoc-related regexp calls

R=rsc
CC=golang-dev
https://golang.org/cl/1987041

src/cmd/godoc/godoc.go

@@ -943,9 +943,9 @@ var (
 
 
 func extractString(src []byte, rx *regexp.Regexp) (s string) {
-	m := rx.Find(src)
-	if len(m) >= 4 {
-		s = strings.TrimSpace(string(src[m[2]:m[3]]))
+	m := rx.FindSubmatch(src)
+	if m != nil {
+		s = strings.TrimSpace(string(m[1]))
 	}
 	return
 }

src/pkg/go/doc/comment.go

@@ -199,7 +199,7 @@ var (
 // and '' into ”).
 func emphasize(w io.Writer, line []byte, words map[string]string, nice bool) {
 	for {
-		m := matchRx.Find(line)
+		m := matchRx.FindSubmatchIndex(line)
 		if m == nil {
 			break
 		}

src/pkg/go/doc/doc.go

@@ -309,7 +309,7 @@ func (doc *docReader) addFile(src *ast.File) {
 	// collect BUG(...) comments
 	for _, c := range src.Comments {
 		text := c.List[0].Text
-		if m := bug_markers.Find(text); m != nil {
+		if m := bug_markers.FindIndex(text); m != nil {
 			// found a BUG comment; maybe empty
 			if btxt := text[m[1]:]; bug_content.Match(btxt) {
 				// non-empty BUG comment; collect comment without BUG prefix