Change GET/GBIT32 macros to explicitly cast final result to u32int.

Otherwise, the type of the expression will be int, and if written to
a uvlong (or just a ulong on most 64-bit systems), it will be
sign-extended.

This was going on in drawfcall with Mouse.msec, which is declared
as a ulong.

This fix assumes that the protocols only send unsigned numbers,
which is true.

include/drawfcall.h

@@ -53,7 +53,7 @@ AUTOLIB(draw)
 	(p)[3] = (x)&0xFF
 
 #define GET(p, x) \
-	((x) = (((p)[0] << 24) | ((p)[1] << 16) | ((p)[2] << 8) | ((p)[3])))
+	((x) = (u32int)(((p)[0] << 24) | ((p)[1] << 16) | ((p)[2] << 8) | ((p)[3])))
 
 #define PUT2(p, x) \
 	(p)[0] = ((x) >> 8)&0xFF, \