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

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

@@ -0,0 +1,13 @@
+contract C {
+    uint[] s;
+    modifier mod(uint[] storage b) {
+        _;
+        b[0] = 0;
+    }
+    function f() mod(a) internal returns (uint[] storage a)
+    {
+		a = s;
+    }
+}
+// ----
+// TypeError: (120-121): This variable is of storage pointer type and can be accessed without prior assignment.