Add 5.2 errata to security.html

Not sure if the one known 5.3 erratum should be listed there already,
or only after the official release.

Index: security.html
===================================================================
RCS file: /cvs/www/security.html,v
retrieving revision 1.394
diff -u -r1.394 security.html
--- security.html	18 Feb 2013 21:48:41 -0000	1.394
+++ security.html	25 Mar 2013 15:54:15 -0000
@@ -248,7 +248,18 @@
 
 <p>
 <ul>
-None yet!
+<li><a href="errata52.html#001_bgpd">November 29, 2012:
+	Some other systems have started sending incorrect flags which cause
+	session failures in OpenBSD's bgpd, and cause it to propagate
+	incorrect updates.
+<li><a href="errata52.html#002_bgpd">March 15, 2013:
+	A rare condition during session startup may cause bgpd to replace
+	an active session leading to unknown consequences.  Bug found by
+	inspection (we do not know how to reproduce it, consider that a challenge).
+<li><a href="errata52.html#003_tftpd">March 21, 2013:
+	A denial of services was discovered where certain combinations of
+	TFTP options could cause OACK generation to fail, which in turn
+	caused a double free in tftpd.
 </ul>
 
 <li>