Natspechandler: Get function hash from transaction data

example/natspec_contract.html

@@ -12,7 +12,7 @@
     // solidity source code
     var source = "" + 
     "contract test {\n" +
-    "   /// @notice This is an awesome function for multiplication. \n" +
+    "   /// @notice Will multiplty `a` by 7. \n" +
     "   function multiply(uint a) returns(uint d) {\n" +
     "       return a * 7;\n" +
     "   }\n" +