develwarn: move config gating inside the develwarn function The config gating is almost always the same and contributor tend to forget it. We move the logic inside the function. Call site will be updated in later changeset. We might make the sub config mandatory in the future (once all old call sites are gone).

help: fix the display for `hg help internals.revlogs` (issue5227) It previously aborted saying the help section wasn't found. Credit to Yuya for figuring out the fix.

builddeb: add distroseries to tagged versions This is needed so that launchpad and friends have a unique version number for each distroseries (trusty, wily, xenial, etc). It was discovered when trying to upload 3.8 to launchpad.