go/doc: add full stop of Japanese, Chinese and Korean.

This fix will show a good synopsis on package listings in that languages.

R=adg, r
CC=golang-dev
https://golang.org/cl/21130043

src/pkg/go/doc/synopsis.go

@@ -22,6 +22,9 @@ func firstSentenceLen(s string) int {
 		if q == ' ' && p == '.' && (!unicode.IsUpper(pp) || unicode.IsUpper(ppp)) {
 			return i
 		}
+		if p == '。' || p == '．' {
+			return i
+		}
 		ppp, pp, p = pp, p, q
 	}
 	return len(s)

src/pkg/go/doc/synopsis_test.go

@@ -28,6 +28,8 @@ var tests = []struct {
 	{"P. Q.   ", 8, "P. Q."},
 	{"Package Καλημέρα κόσμε.", 36, "Package Καλημέρα κόσμε."},
 	{"Package こんにちは 世界\n", 31, "Package こんにちは 世界"},
+	{"Package こんにちは。世界", 26, "Package こんにちは。"},
+	{"Package 안녕．世界", 17, "Package 안녕．"},
 	{"Package foo does bar.", 21, "Package foo does bar."},
 	{"Copyright 2012 Google, Inc. Package foo does bar.", 27, ""},
 	{"All Rights reserved. Package foo does bar.", 20, ""},