rust-dirstate: rename NULL_REVISION to NULL_ID which isn't a revision number

rust-dirstate: remove repetition in array literal

rust-dirstate: remove too abstracted way of getting &[u8]

rust-dirstate: remove unneeded "ref" At 7cae6bc29ff9, .to_owned() was rewritten as .to_owned().to_vec(), which is no longer needed since the filename is a single reference.

rust-parsers: fix unboxing of PyInt on Python 3 Broken at 7cae6bc29ff9.

revlog: split `rawtext` retrieval out of _revisiondata This part is reasonably independent. Having it on its own clarify the code flow and will help code that inherit from revlog to overwrite specific area only.

revlog: avoid caching raw text too early in _revisiondata Without this change, we could cache the rawtext without considering for it validating the cache or not. If the exception raised by the invalid hash were to be caught and the same revision accessed again, the invalid rawtext would be returned.

revlog: add some documentation to `_revisiondata` code

revlog: move `nullid` early return sooner in `_revisiondata` Let us deal with the special case before we start dealing with more generic case.

revlog: stop calling `basetext` `rawtext` in _revisiondata If the cache entry is used as a base test for delta, it is not the rawtext we need. We update the variable name to clarify this.