The Application class unfortunately insists that every
requested resource must be a real filesystem resource,
but this limitation doesn't let servlet factories work
out whether they can handle such requests anyway.
For example, one might want to serve "default.py" when
any non-existent .py resource is requested within a
given context and to implement this mechanism in a
servlet factory. These non-existent resources could be
called "virtual" resources and are reminiscent of
mod_python's handler semantics.
This patch tentatively removes the "real resource"
limitation in the 0.8 release version of Application.