repoview: rename '_getdynamicblockers' to 'revealedrevs' (API) Recent mailing list discussion made me realised we could clarify these. We make the function "public" to encourage extensions to wrap it and we use a more explicit name that mirror "hideablerevs".

repoview: move '_getdynamicblock' next to 'hideablerevs' There are the two functions that extensions should use to augment the hidding logic. It seem better to have them together at the top of the file.

python3: allow hgloader to work with lazy loaders Don't clobber the loader returned from find_spec. This brings `hg version` down from 0.27 seconds to 0.17.

init: turn on demandimport for Python 3.6 and above This uses the new demandimport implementation for Python 3 introduced in previous patches. This doesn't yet enhance performance because it isn't integrated with the custom source file loader we use on Python 3. We'll integrate the two in upcoming patches.

demandimport: add python 3 implementation This implementation uses the new importlib finder/loader functionality available in Python 3.5 and up. # no-check-commit

demandimport: move ignore list to __init__.py We're going to use the same ignore list for Python 3.