The error messages that pyflakes outputs dont contain enough information
to classify them as errors or warnings. Apart from checking for all
known warning outputs and classifying the rest as errors (or vice versa)
there is no way classify.
Make the syntax checker class all results as errors. Individual warning
formats can be checked for later if they become a problem.
This addresses #189.
dont refer to g:syntastic_python_checker since - due to a previous
commit - this is not guaranteed to exist any more.
This change should have been done in the aforementioned commit - but I
failed.