Using gunicorn with paster command line causes the application to
load before gunicorn. In this case, there is no choice but to preload
the application. Document this fact.
Fixes#528.
It is now possible to specify a file with "config" as an application
configuration key in a paste deploy configuration file. This allows
paster applications to use the full range of gunicorn settings even
when using paste/pserve rather than gunicorn_paster.
Fixes#540.
