Add push() for dynamic storage arrays

test/libsolidity/semanticTests/array/push_no_args_2d.sol

@@ -0,0 +1,39 @@
+contract C {
+	uint[][] array2d;
+
+	function l() public returns (uint) {
+		return array2d.length;
+	}
+
+	function ll(uint index) public returns (uint) {
+		return array2d[index].length;
+	}
+
+	function a(uint i, uint j) public returns (uint) {
+		return array2d[i][j];
+	}
+
+	function f(uint index, uint value) public {
+		uint[] storage pointer = array2d.push();
+		for (uint i = 0; i <= index; ++i)
+			pointer.push();
+		pointer[index] = value;
+	}
+
+	function lv(uint value) public {
+		array2d.push().push() = value;
+	}
+}
+// ----
+// l() -> 0
+// f(uint256,uint256): 42, 64 ->
+// l() -> 1
+// ll(uint256): 0 -> 43
+// a(uint256,uint256): 0, 42 -> 64
+// f(uint256,uint256): 84, 128 ->
+// l() -> 2
+// ll(uint256): 1 -> 85
+// a(uint256,uint256): 0, 42 -> 64
+// a(uint256,uint256): 1, 84 -> 128
+// lv(uint256): 512 ->
+// a(uint256,uint256): 2, 0 -> 512