Modifies WaitEvent and WaitEventTimeout to actually wait instead of polling

When possible use native os functions to make a blocking call waiting for
an incoming event. Previous behavior was to continuously poll the event
queue with a small delay between each poll.

The blocking call uses a new optional video driver event,
WaitEventTimeout, if available. It is called only if an window
already shown is available. If present the window is designated
using the variable wakeup_window to receive a wakeup event if
needed.

The WaitEventTimeout function accept a timeout parameter. If
positive the call will wait for an event or return if the timeout
expired without any event. If the timeout is zero it will
implement a polling behavior. If the timeout is negative the
function will block indefinetely waiting for an event.

To let the main thread sees events sent form a different thread
a "wake-up" signal is sent to the main thread if the main thread
is in a blocking state. The wake-up event is sent to the designated
wakeup_window if present.

The wake-up event is sent only if the PushEvent call is coming
from a different thread. Before sending the wake-up event
the ID of the thread making the blocking call is saved using the
variable blocking_thread_id and it is compared to the current
thread's id to decide if the wake-up event should be sent.

Two new optional video device methods are introduced:

WaitEventTimeout
SendWakeupEvent

in addition the mutex

wakeup_lock

which is defined and initialized but only for the drivers supporting the
methods above.

If the methods are not present the system behaves as previously
performing a periodic polling of the events queue.

The blocking call is disabled if a joystick or sensor is detected
and falls back to previous behavior.

test/Makefile.in

@@ -9,6 +9,7 @@ LIBS	= @LIBS@
 
 TARGETS = \
 	checkkeys$(EXE) \
+	checkkeysthreads$(EXE) \
 	controllermap$(EXE) \
 	loopwave$(EXE) \
 	loopwavequeue$(EXE) \
@@ -83,6 +84,9 @@ Makefile: $(srcdir)/Makefile.in
 checkkeys$(EXE): $(srcdir)/checkkeys.c
 	$(CC) -o $@ $^ $(CFLAGS) $(LIBS)
 
+checkkeysthreads$(EXE): $(srcdir)/checkkeysthreads.c
+	$(CC) -o $@ $^ $(CFLAGS) $(LIBS)
+
 loopwave$(EXE): $(srcdir)/loopwave.c
 	$(CC) -o $@ $^ $(CFLAGS) $(LIBS)