Provide python logging compatibility in eventlet.wsgi

Provide a compatibility layer in eventlet.wsgi that allows you
to hand a python logger as the log parameter instead of a
filehandle. This is done via an object wrapper so the logging
methods will only be used if the contents of the log parameter
look like a log, otherwise the previous behavior of just writing
to the logger is done instead.

(This is work in progress patch to make sure the approach is
ok. Can add unit tests in future revision.)