rust-cpython: consistency in use of hg-core constructs
While not everybody likes the `CoreLazy` and `CoreIterator`
aliases, it's better not to mix them with direct references.
Note: it's quite possible in the future that these would stop
being exposed at the top of the `hg` crate
Differential Revision: https://phab.mercurial-scm.org/D5547
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown