hgweb: simplify the handling of empty repo This abstraction have two advantages: - If the revlog is empty, None of the code bellow is relevant, early returns seems a win. - Abtraction of the 'emptiness' check will help later when we stop relying on nodefunc. A bonus, with filtering, a non-empty revlog may not have '0' revision accessible. It'll be easier to handle with the emptiness test in a dedicated function

hgweb: move hex creation into an object method This is clearer and allow later overwrite.

hgweb: pass nodefunc to the revnav object The issue between hgweb and filtering lay in this function. Moving it into the object itself helps to abstract the erroneous bit.

hgweb: move revnavgen into an object For later compatibility with changelog filtering some part of the navigation generation logic will be altered. Those altered part will be different when in the changelog case and in the filelog case. Moving this into an object will allow to use inheritance to override just the part of the logic we need. The aimed logic are for example: - generation of revision 'hex' (different logic for changelog and filelog) - revlog emptyness test - fetching of the first revision of a revlog (may not be 0)

hgweb: `limit` argument is actually `latestonly` renames and enforce The `limit` argument of several generator have only two possible values in practice: 0 and 1. We rename this parameter to `latestonly` and simplify it's handling. The simplification allows us to save fetching of data that we are sure to not consume. Having a function minimal function perimeter will helps future refactoring.

hgweb: add test regarding filtering and hgweb Since 4d1671b39168 hgweb is broken with filtering. This changeset add test that should pass once it is fixed. Test currently broken are commented and will be uncommented by changeset that fix them. The filelog test is currently passing because we already have some hack in core regarding filelog (see 518c1403838f).

get-with-headers: add a --headeronly switch In some case we do not care about the actual rendering.

tests: more comment cleanup related to obsolescence

test: fix in-test comments related to obsolescence The `ui.prevent-unstable` option never made it into core. It always behaves this way when obsolescence feature is enabled. See changesets c5bd753c5bc6, bacf55bd8f90 and 0f5a0a2073a8 for details.

stream_in: write the remote branchcache for a usage as wide as possible Writing cache for unfiltered repo only is barely useful, Most repo user are now at least use the `hidden` filter. This changeset now assigns the remote cache for a filter as low as possible for a wider reuse as possible.