Refactoring of the ControlFlowGraph and use for detecting all uninitialized storage accesses.

test/libsolidity/syntaxTests/controlFlow/uninitializedAccess/modifier_order_fail.sol

@@ -0,0 +1,8 @@
+contract C {
+    modifier m1(uint[] storage a) { _; }
+    modifier m2(uint[] storage a) { _; }
+    uint[] s;
+    function f() m1(b) m2(b = s) internal view returns (uint[] storage b) {}
+}
+// ----
+// TypeError: (129-130): This variable is of storage pointer type and can be accessed without prior assignment.