Allow duplicated constructor calls, if no arguments; support for multiple inheritance; backwards compatibility.

# tmp

test/libsolidity/syntaxTests/inheritance/allow_empty_duplicated_super_constructor_call.sol

@@ -0,0 +1,3 @@
+contract A { constructor() public { } }
+contract B1 is A { constructor() A() public {  } }
+contract B2 is A { constructor() A public {  } }

test/libsolidity/syntaxTests/inheritance/base_arguments_multiple_inheritance.sol

@@ -0,0 +1,9 @@
+contract Base {
+    constructor(uint) public { }
+}
+contract Base1 is Base(3) {}
+contract Derived is Base, Base1 {
+    constructor(uint i) Base(i) public {}
+}
+// ----
+// Warning: Duplicated super constructor calls are deprecated.

test/libsolidity/syntaxTests/inheritance/duplicated_ancestor_constructor_call.sol

@@ -0,0 +1,5 @@
+contract A { constructor(uint) public { } }
+contract B is A(2) { constructor() public {  } }
+contract C is B { constructor() A(3) public {  } }
+// ----
+// Warning: Duplicated super constructor calls are deprecated.

test/libsolidity/syntaxTests/inheritance/duplicated_ancestor_constructor_call_V050.sol

@@ -0,0 +1,7 @@
+pragma experimental "v0.5.0";
+
+contract A { constructor(uint) public { } }
+contract B is A(2) { constructor() public {  } }
+contract C is B { constructor() A(3) public {  } }
+// ----
+// DeclarationError: Duplicated super constructor call.

test/libsolidity/syntaxTests/inheritance/duplicated_super_constructor_call.sol

@@ -1,4 +1,4 @@
 contract A { constructor(uint) public { } }
 contract B is A(2) { constructor() A(3) public {  } }
 // ----
-// DeclarationError: Duplicated super constructor call.
+// Warning: Duplicated super constructor calls are deprecated.

test/libsolidity/syntaxTests/inheritance/duplicated_super_constructor_call_V050.sol

@@ -0,0 +1,6 @@
+pragma experimental "v0.5.0";
+
+contract A { constructor(uint) public { } }
+contract B is A(2) { constructor() A(3) public {  } }
+// ----
+// DeclarationError: Duplicated super constructor call.

test/libsolidity/syntaxTests/inheritance/duplicated_super_constructor_call_empty.sol

@@ -1,4 +0,0 @@
-contract A { constructor() public { } }
-contract B is A { constructor() A() public {  } }
-// ----
-// DeclarationError: Duplicated super constructor call.

test/libsolidity/syntaxTests/inheritance/duplicated_super_constructor_call_multi.sol

@@ -0,0 +1,7 @@
+contract C { constructor(uint) public {} }
+contract A is C(2) {}
+contract B is C(2) {}
+contract D is A, B { constructor() C(3) public {} }
+// ----
+// Warning: Duplicated super constructor calls are deprecated.
+// Warning: Duplicated super constructor calls are deprecated.