mercurial/parsers.c: fix compiler warning

When try to compile on x64 OS X, I get this warning:

mercurial/parsers.c:931:27: warning: implicit conversion loses integer precision
: 'long' to 'int' [-Wshorten-64-to-32]
                        ? 4 : self->raw_length / 2;

The patch verifies if value of self->raw_length falls bellow INT_MAX; if not,
it raises the ValueError exception.

If value of self->raw_length is greater than 4, it's casted to int type, to
eliminate the warning.

mercurial/parsers.c

@@ -927,8 +927,13 b' static int nt_insert(indexObject *self, '
 static int nt_init(indexObject *self)
 {
 	if (self->nt == NULL) {
+		if (self->raw_length > INT_MAX) {
+			PyErr_SetString(PyExc_ValueError, "overflow in nt_init");
+			return -1;
+		}
 		self->ntcapacity = self->raw_length < 4
-			? 4 : self->raw_length / 2;
+			? 4 : (int)self->raw_length / 2;
+
 		self->nt = calloc(self->ntcapacity, sizeof(nodetree));
 		if (self->nt == NULL) {
 			PyErr_NoMemory();