Warn if modifiers are applied to functions without implementation.

test/libsolidity/syntaxTests/modifiers/modifiers_on_abstract_functions_050.sol

@@ -0,0 +1,10 @@
+pragma experimental "v0.5.0";
+contract C
+{
+    modifier only_owner() { _; }
+    function foo() only_owner public;
+    function bar() public only_owner;
+}
+// ----
+// SyntaxError: (80-113): Functions without implementation cannot have modifiers.
+// SyntaxError: (118-151): Functions without implementation cannot have modifiers.

test/libsolidity/syntaxTests/modifiers/modifiers_on_abstract_functions_no_parser_error.sol

@@ -0,0 +1,13 @@
+// Previous versions of Solidity turned this
+// into a parser error (they wrongly recognized
+// these functions as state variables of
+// function type).
+contract C
+{
+    modifier only_owner() { _; }
+    function foo() only_owner public;
+    function bar() public only_owner;
+}
+// ----
+// Warning: (203-236): Modifiers of functions without implementation are ignored.
+// Warning: (241-274): Modifiers of functions without implementation are ignored.