Use enum wl_pointer_button_state instead of integer

Instead of using a uint32_t for state everywhere (except on the wire,
where that's still the call signature), use the new
wl_pointer_button_state enum, and explicit comparisons.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
diff --git a/clients/dnd.c b/clients/dnd.c
index c6f0f18..b6720f0 100644
--- a/clients/dnd.c
+++ b/clients/dnd.c
@@ -358,7 +358,8 @@
 static void
 dnd_button_handler(struct widget *widget,
 		   struct input *input, uint32_t time,
-		   uint32_t button, uint32_t state, void *data)
+		   uint32_t button, enum wl_pointer_button_state state,
+		   void *data)
 {
 	struct dnd *dnd = data;
 	int32_t x, y;
@@ -378,7 +379,7 @@
 	x -= allocation.x;
 	y -= allocation.y;
 
-	if (item && state == 1) {
+	if (item && state == WL_POINTER_BUTTON_STATE_PRESSED) {
 		dnd_drag = malloc(sizeof *dnd_drag);
 		dnd_drag->dnd = dnd;
 		dnd_drag->input = input;