Merge pull request #3722 from ethereum/fixMods

Fix modifier lookup in libraries.

test/libsolidity/syntaxTests/virtualLookup/modifiers_in_libraries.sol

@@ -0,0 +1,14 @@
+library WithModifier {
+    modifier mod() { require(msg.value > 10 ether); _; }
+    function withMod(uint self) mod() internal view { require(self > 0); }
+}
+
+contract Test {
+    using WithModifier for *;
+
+    function f(uint _value) public payable {
+        _value.withMod();
+        WithModifier.withMod(_value);
+    }
+}
+// ----