dirstate-item: introduce low level C function
Since a lot of logic is about to change, we need to isolate it into bits that
are easy reusable in the rest of the C code.
Especially we need to split the part that do the pure logic from the part that
do the Python wrapping.
Differential Revision: https://phab.mercurial-scm.org/D11386
[workspace]
members = ["hg-core", "hg-cpython", "rhg"]
exclude = ["chg", "hgcli"]