By default, gevent prints exceptions and tracebacks to stderr. This is
obnoxious as it results in large tracebacks intermixed with the output
that the logger prints to the console. This commit redirects this data
to {DATA_DIR}/gevent_exceptions.log. Unfortunately, this would mean that
the user might be left without any indication these exceptions had
occurred, unless they take the time to inspect the
gevent_exceptions.log. Therefore, when an excepion occurs, a message
with just the exception (not the traceback) is logged to WARNING.
Fixes#859
Mike Salvatore
Shreya
VakarisZ