Passed the engine instance to loaders. This is a prerequisite for
looking up configuration on the engine instance instead of global
settings.
This is backwards incompatible for custom template loaders that override
__init__. However the documentation doesn't talk about __init__ and the
way to pass arguments to custom template loaders isn't specified. I'm
considering it a private API.
Reformatted the code of base.Loader according to modern standards.
Turned the test template loader into a regular locmem.Loader -- but
didn't document it.
Added a normal deprecation path for BaseLoader which is a public API.
Added an accelerated deprecation path for TestTemplateLoader which is
a private API.
Preston Timmons
Aymeric Augustin