rust: propagate error of index_get_parents() properly Before, rustla_contains() would return 0 on error, and the exception would be cleared or noticed somewhere else. We need to propagate the error from AncestorsIterator up to the FFI surface.

rust: look up HgRevlogIndex_GetParents() from symbol table And removes the unused index_get_parents_checked() function. I expect the Index struct will be turned into a pyobject type, though I haven't written any PoC-level patches yet.

revlog: add public CPython function to get parent revisions Since this is a public function, it validates the input revision, and supports nullrev. index_get_parents_checked() will be replaced by this function.

revlog: rename indexType to HgRevlogIndex_Type as it's a global symbol It follows the CPython naming convention, but uses Hg instead of Py.

revlog: export symbol of indexType The idea is to wrap the index object with rust-cpython. I haven't tried it, but it should be doable. We'll probably need a better interface than raw function pointers to do more in Rust.

setup: fix path of rust source dependencies Appears that they were screwed up while moving the source files around. Since rust-direct-ffi sources are automatically added to the depends list, we only need to list hg-core sources.

rebase: remove now-unnecessary arguments to _abort() Since _abort() is now an instance method, we don't need to pass state that's available on "self". Differential Revision: https://phab.mercurial-scm.org/D5393