hgweb: show instabilities of a commit In paper, coal, gitweb and monoblue a new "tag" (or multiple, if there are many instabilities) is added to the same line that has phase, branch, etc of a changeset; in gitweb and monoblue this element has a light red background, in paper and coal the element is black and underlined. In spartan theme instabilities are shown on a separate line. While test-obsolete.t uses first(phasedivergent()) revset to pick a changeset to test, that particular changeset is also an orphan, so two different instability tags are displayed.

context: add instabilities() method to basefilectx This method is now used in webutils.commonentry(), which adds common data items (commit hash, author, date, etc) for rendering changesets in hgweb. Usually, commonentry() is given a changectx as ctx; but in views related to files (e.g. file view, diff, annotate) it's replaced by a filectx, so the latter also needs to have instabilities() method.