Basic support for QEMU Extended Key Events

This adds the basic infrastructure and handshake for the QEMU
Extended Key Events extension. No viewer or server makes use of
the extra functionality yet though.
diff --git a/common/rfb/CMsgReader.cxx b/common/rfb/CMsgReader.cxx
index 0aaf71f..eee6d27 100644
--- a/common/rfb/CMsgReader.cxx
+++ b/common/rfb/CMsgReader.cxx
@@ -111,6 +111,8 @@
       break;
     case pseudoEncodingLEDState:
       readLEDState();
+    case pseudoEncodingQEMUKeyEvent:
+      handler->supportsQEMUKeyEvent();
       break;
     default:
       readRect(Rect(x, y, x+w, y+h), encoding);