tests: make custom templates that use {whyunstable} terser These templates demonstrate that {whyunstable} is fully template-friendly, but they don't need to produce such long lines of output.

tests: hg log shouldn't need --hidden to show whyunstable template keyword

makefile: add Ubuntu Bionic docker targets (.deb and ppa) Bionic Beaver is an LTS release, supported until 2023-04.

makefile: reformat .PHONY targets The list of make targets is likely to evolve over time. This reformats streamlines future patches.

makefile: mkdir is not needed on templatized docker builds This imitates e63dfbbdbd07 and is a small addition to 231690dba9b4 and 5c1283713293

hgweb: convert _siblings to a factory function of mappinggenerator IIUC, only reason it was a class is to make the generator restartable, which is now served by the mappinggenerator.

hgweb: extract a generator function of _siblings class _siblings will be converted to a plain function.

hgweb: wrap {changenav} and {nav} with mappinglist

hgweb: make revnav.gen() simply build a list of mappings by one pass There was actually no lazy stuff.

hgweb: lift {sessionvars} to a wrapped type Since a sessionvars object is updated in-place, we can't simply wrap it by mappinglist.

hgweb: make sessionvars class less dense

hgweb: prefix private variables of sessionvars with '_'

lfs: update the HTTP status codes in error cases I'm not bothering with validating PUT requests (for now), because the spec doesn't explicitly call out a Content-Type (though the example transcript does use the sensible 'application/octet-stream').

lfs: gracefully handle aborts on the server when corrupt blobs are detected The aborts weren't killing the server, but this seems cleaner. I'm not sure if it matters to handle the remaining IOError in the test like this, for consistency. The error code still feels wrong (especially if the client is trying to download a corrupt blob) but I don't see anything better in the RFCs, and this is already used elsewhere because the Batch API spec specifically mentioned this as a "Validation Error".