Make the currently-skipped known-failing test actually fail.

Before it was marked as skipped until we could fix it, but if you
forced it to run, it should print out a panic stack trace and then say
PASS. So this makes it actually fail.

Actual fix coming later, now that we have an actual failing list.
diff --git a/server.go b/server.go
index 4637818..256aa9c 100644
--- a/server.go
+++ b/server.go
@@ -55,6 +55,7 @@
 var (
 	testHookOnConn        func()
 	testHookGetServerConn func(*serverConn)
+	testHookOnPanic       func(sc *serverConn, panicVal interface{}) (rePanic bool)
 )
 
 // TODO: finish GOAWAY support. Consider each incoming frame type and
@@ -450,8 +451,19 @@
 	}
 }
 
+func (sc *serverConn) notePanic() {
+	if testHookOnPanic != nil {
+		if e := recover(); e != nil {
+			if testHookOnPanic(sc, e) {
+				panic(e)
+			}
+		}
+	}
+}
+
 func (sc *serverConn) serve() {
 	sc.serveG.check()
+	defer sc.notePanic()
 	defer sc.conn.Close()
 	defer sc.closeAllStreamsOnConnClose()
 	defer sc.stopShutdownTimer()