0.8dev: Use fully-qualified name for `request_factory` and `environment_factory`. Refs #795.

 * For the typically multiproduct environment, `[trac] environment_factory = multiproduct.hooks.MultiProductEnvironmentFactory` and `[trac] request_factory = multiproduct.hooks.ProductRequestFactory`.
 * Use `abc` module for abstract base classes.


git-svn-id: https://svn.apache.org/repos/asf/bloodhound/trunk@1616400 13f79535-47bb-0310-9956-ffa450edef68