TQPathManger should print warning if file cannot be found
Currently, when trying to find an (input) file using the TQPathManager we can end up with difficult to understand errors. Since TQPathManager::findFileFromEnvVar returns an empty string if some file is neither found in a relative path nor within the directory given by the env var we typically end up with errors of the form 'No such file ""(empty string)'. This is obviously not very helpful. I suggest to add a warning printout to the aforementioned TQPM method including the input file name/path that was passed to the method.
If someone can envision a use case where the non-existence of a file can be expected (e.g. just testing for the presence of such a file), I suggest to add an optional boolean argument to the method (bool silent=false).