largefile: use `update_file` instead of `normallookup` in `updatelfiles`
This is the newer, more semantic API.
Differential Revision: https://phab.mercurial-scm.org/D11164
dirstate: add a `set_possibly_dirty` method
This method will be able to replace some usage of `normallookup` in the future.
Differential Revision: https://phab.mercurial-scm.org/D11162