AT ENTRY trigger is not injected unless class is compiled with line number info included

If a target class is compiled without line number information then an AT ENTRY trigger fails to match the target method. This is counter-intuitive since there is no need to know what line the method starts on in order to know that it starts somewhere.

This is actually because the AT ENTRY location specifier is treated internally as if it were an AT LINE -1 location specifier. This is a cheap hack which allows AT ENTRY injection to be done using the same mechanism as implements AT LINE injection. When the AT LINE trigger injector's visitLineNUmber method is first called for a matching method it identifies that the visited line number > -1 and so marks the current bytecode location as the trigger point. The only problem is that in the absence of line number information the visitLineNumber method never gets called.