We recently introduced a dedicated type for index entries in the
pure Python implementation.
This commit tells the revlog C code about that type.
We register the type on the parsers module so it is exposed to
importers of the module.
In addition, we store a reference to the type on revlog index
instances. In theory, we could grab the reference from the
module. However, this requires a fair bit of C code. It is easier
to just re-import the original module and get a ref from there. This
also avoids problems with caching a type on a reload()d module.