Test for sign bit chopping.

test/libsolidity/semanticTests/storage/chop_sign_bits.sol

@@ -0,0 +1,29 @@
+contract Test {
+    int16[] public x = [-1, -2];
+    int16[2] public y = [-5, -6];
+    int16 z;
+    function f() public returns (int16[] memory) {
+        int8[] memory t = new int8[](2);
+        t[0] = -3;
+        t[1] = -4;
+        x = t;
+        return x;
+    }
+    function g() public returns (int16[2] memory) {
+        int8[2] memory t = [-3, -4];
+        y = t;
+        return y;
+    }
+    function h(int8 t) public returns (int16) {
+        z = t;
+        return z;
+    }
+}
+// ----
+// x(uint256): 0 -> -1
+// x(uint256): 1 -> -2
+// y(uint256): 0 -> -5
+// y(uint256): 1 -> -6
+// f() -> 0x20, 2, -3, -4
+// g() -> -3, -4
+// h(int8): -10 -> -10