fix puts on existing directories in irodsstorage

make the write() fucntion not only check for existing files,
but also for directories at the place we want to write.
There is no distinction in the error reporting.
fix errorhandling in irodsstorage

1. add a handle_error function to manage them centrally
2. remove checks for parent directories, as we cannot
  get any reasonable error codes from that except NotFound.
  It has to stay in ls() at the moment - no idea how to
  replace that yet.
3. Introduce the IsFileException
add error message logging with path to localstorage exception handling