goprotobuf: Miscellaneous fixes.

- Support single quoted strings.
- Allow declaring import path to hint at a package name.

R=r
CC=golang-dev
http://codereview.appspot.com/6366043
diff --git a/proto/text_parser_test.go b/proto/text_parser_test.go
index bca0ecb..65211a6 100644
--- a/proto/text_parser_test.go
+++ b/proto/text_parser_test.go
@@ -111,6 +111,15 @@
 		},
 	},
 
+	// Quoted string with single quote
+	{
+		in: `count:42 name: 'Roger "The Ramster" Ramjet'`,
+		out: &MyMessage{
+			Count: Int32(42),
+			Name:  String(`Roger "The Ramster" Ramjet`),
+		},
+	},
+
 	// Bad quoted string
 	{
 		in:  `inner: < host: "\0" >` + "\n",