fix channel multiple close bug and concurrency bug in the way sessionInfo.close was being called

src/yggdrasil/conn.go

@@ -256,7 +256,7 @@ func (c *Conn) Close() error {
 	defer c.mutex.Unlock()
 	if c.session != nil {
 		// Close the session, if it hasn't been closed already
-		c.session.close()
+		c.core.router.doAdmin(c.session.close)
 	}
 	// This can't fail yet - TODO?
 	c.closed = true

src/yggdrasil/session.go

@@ -269,8 +269,11 @@ func (ss *sessions) cleanup() {
 
 // Closes a session, removing it from sessions maps and killing the worker goroutine.
 func (sinfo *sessionInfo) close() {
+	if s := sinfo.core.sessions.sinfos[sinfo.myHandle]; s == sinfo {
 		delete(sinfo.core.sessions.sinfos, sinfo.myHandle)
 		delete(sinfo.core.sessions.byTheirPerm, sinfo.theirPermPub)
+	}
+	defer func() { recover() }()
 	close(sinfo.worker)
 }