goprotobuf: Update .hgtags.

Point go.r60 at tip, and add weekly.2011-09-21.

R=adg, r
CC=golang-dev
http://codereview.appspot.com/5150045

.hgtags

@@ -12,5 +12,6 @@ fa1080cfc0a4d0fa24844bc50124aed892365059 release.r57.2
 cfe37a63cede6cd072434965e6ea426b90bcb223 release.r58
 cfe37a63cede6cd072434965e6ea426b90bcb223 release.r58.1
 da17c98c73d8801baa1d2e493c9ac0844470ef0a release.r59
-5a487ccac6f7fd6cba5deee5d5d0908c7f1d6a53 go.r60
+bc76a153ffde5de8535b7c2791102ddd0b93f187 go.r60
 5a487ccac6f7fd6cba5deee5d5d0908c7f1d6a53 go.weekly.2011-09-07
+bc76a153ffde5de8535b7c2791102ddd0b93f187 go.weekly.2011-09-21