[client] allow frame updates to be triggered by a timed event

This is a major change to how the LG client performs it's updates. In
the past LG would operate a fixed FPS regardless of incoming update
speed and/or frequency. This change allows LG to dynamically increase
it's FPS in order to better sync with the guest as it's rate changes.

common/include/common/event.h

@@ -20,6 +20,7 @@ Place, Suite 330, Boston, MA 02111-1307 USA
 #pragma once
 
 #include <stdbool.h>
+#include <time.h>
 
 #define TIMEOUT_INFINITE ((unsigned int)~0)
 
@@ -34,4 +35,8 @@ bool      lgResetEvent (LGEvent * handle);
 
 // os specific method to wrap/convert a native event into a LGEvent
 // for windows this is an event HANDLE
-LGEvent * lgWrapEvent(void * handle);
+LGEvent * lgWrapEvent(void * handle);
+
+// Posix specific, not implmented/possible in windows
+bool lgWaitEventAbs(LGEvent * handle, struct timespec * ts);
+bool lgWaitEventNS (LGEvent * handle, unsigned int timeout);