Enable working as wsgi application of standard web server (Apache)

This blueprint focuses on enabling Swift to run as a wsgi application of Apache via mod_wsgi, but is designed to also address the more general need to allow using a fully features web server as a front end of open stack components.

A thin wsgi interface is added in openstack common files, enabling open-stack components to interface a standard web server (E.g. Apache2) via wsgi.
Using this interface, a standard mature and full fledged web server can be used as a web front end, feeding the openstack components via standard wsgi interface.
This interface therefore offers an option (but does not mandate) to replace the current python web front end with a standard web server.
Alternatively, it offers a more efficient interface between a web server and the openstack components.

In order for an openstack component to work as a wsgi application, the component needs to comply with the wsgi standard. For example Apache with mod_wsgi is not forgiving to certain violations of the standard.
Included in this work is a set of bug fixes to get the swift code to comply with the wsgi standard and work with Apache mod_wsgi.
The interface and bug fixes aim to maintain the current Swift functionality, while measured performance in swift using the existing web front end and an alternative Apache are comparable.