xdiff: silence a 32-bit shift warning on Windows

It's probably harmless, but:

    warning C4334: '<<' : result of 32-bit shift implicitly converted to 64 bits
    (was 64-bit shift intended?)

Adding a 'ULL' suffix to 1 also works, but I doubt that's portable.

mercurial/thirdparty/xdiff/xprepare.c

@@ -71,7 +71,7 b' static int xdl_init_classifier(xdlclassi'
 	cf->flags = flags;
 
 	cf->hbits = xdl_hashbits(size);
-	cf->hsize = 1 << cf->hbits;
+	cf->hsize = ((uint64_t)1) << cf->hbits;
 
 	if (xdl_cha_init(&cf->ncha, sizeof(xdlclass_t), size / 4 + 1) < 0) {
 
@@ -263,7 +263,7 b' static int xdl_prepare_ctx(unsigned int '
 
 	{
 		hbits = xdl_hashbits(narec);
-		hsize = 1 << hbits;
+		hsize = ((uint64_t)1) << hbits;
 		if (!(rhash = (xrecord_t **) xdl_malloc(hsize * sizeof(xrecord_t *))))
 			goto abort;
 		memset(rhash, 0, hsize * sizeof(xrecord_t *));