manifest: move dirlog up to manifestrevlog
This removes dirlog and its associated cache from manifest and puts it in
manifestrevlog. The notion of there being sub-logs is specific to the revlog
implementation, and therefore belongs on the revlog class.
This patch will enable future patches to move the serialization logic for
manifests onto manifestrevlog, which will allow us to move manifest.add onto
manifestlog in a way that it just calls out to manifestrevlog for the
serialization.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.