hgtags: add release tag, again.

R=r
https://golang.org/cl/170049
diff --git a/.hgtags b/.hgtags
index 00f8dce..62db726 100644
--- a/.hgtags
+++ b/.hgtags
@@ -5,3 +5,4 @@
 d1b75410b793309532352a6fb6b44453f052f3f4 release.2009-11-17
 e205103b02e7393d4719df5faac2dac808234d3f release.2009-12-07
 3a47d2e3882bb12129de05382a2c131bb0c00964 release.2009-12-09
+7929874a70aecc714d5fad4ae1529b1352db6d70 release