rust-index: add a function to convert PyObject index for hg-core Function in hg-core need something implementing the `Graph` trait. Right now, the `hg-cpython` entry points directly turn the PyObject passed as argument into a `cindex::Index`. However, if we start having the option to use an Index in Rust, we need to dispatch between the different possible PyObject we could receive. So move the "duplicate" call into a unified function. When time come. It will be easy to update the logic of all interface when the time come. Differential Revision: https://phab.mercurial-scm.org/D7653

--- a/rust/hg-cpython/src/lib.rs	Wed Dec 11 18:40:04 2019 +0100
+++ b/rust/hg-cpython/src/lib.rs	Fri Dec 13 19:59:59 2019 +0100
@@ -35,6 +35,7 @@
 pub mod exceptions;
 pub mod filepatterns;
 pub mod parsers;
+pub mod revlog;
 pub mod utils;
 
 py_module_initializer!(rustext, initrustext, PyInit_rustext, |py, m| {