Disallow explicit conversions from negative literals to `address`

test/libsolidity/syntaxTests/types/address/conversion.sol

@@ -0,0 +1,9 @@
+contract C {
+    function f() public pure returns (address) {
+        return address(2**160 -1);
+    }
+    function g() public pure returns (address) {
+        return address(uint(-1));
+    }
+}
+// ----

test/libsolidity/syntaxTests/types/address/conversion_error.sol

@@ -0,0 +1,15 @@
+contract C {
+    function f() public pure returns (address) {
+        return address(-1);
+    }
+    function g() public pure returns (address) {
+        return -1;
+    }
+	function h() public pure returns (address) {
+		return address(2**160);
+	}
+}
+// ----
+// TypeError 9640: (77-88): Explicit type conversion not allowed from "int_const -1" to "address".
+// TypeError 6359: (160-162): Return argument type int_const -1 is not implicitly convertible to expected type (type of first return variable) address.
+// TypeError 9640: (225-240): Explicit type conversion not allowed from "int_const 1461...(41 digits omitted)...2976" to "address".