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.