tests: avoid repr in test-bundle2-format.t We don't *really* need it here, and it was making Python 3 harder.

tests: port test-bundle2-format inline helper script to Python 3 We're now very close to this test passing.

bundle2: portably grab first byte of part name for letter check

bundle2: make ValueError messages native strings

bundle2: update check for a generator to work on Python 3

bundle2: stop using %r to quote part names Valid part names are restricted to [a-zA-Z0-9_:-]+, so I'm not worried about having quoting present in places where we should have predominantly valid part names. This will significantly ease the Python 3 transition, and simultaneously isn't a BC because this is only in error messages that should never be shown.

blackbox: set lastui even if ui.log is not called (issue5518) `lastui` decides where (where is the `.hg`) to use if the current `ui` object does not have a `_bbrepo` associated. Previously it only gets set in `ui.log`, which means unless a `ui` with repo associated calls `log` with tracked event, blackbox does not know where to write its log. This patch makes `reposetup` set `lastui` so it so we could log some more events (see test changes). Differential Revision: https://phab.mercurial-scm.org/D655