context: only bother looking for broken dirstate for 20-byte changeid If we fail to look up a changeid in changectx.__init__, we check if it exactly matches any of the dirstate parents, and if it does, we print a more specific message ("working directory has unknown parent '...'!" instead of "unknown revision '...'"). The dirstate parents are always 20 bytes, so there's no need to check for a match when the given changeid is not 20 bytes. (And now that all the other allowed forms of changeid have been moved out of the constructor, there's no risk that a changeid that did match a dirstate parent was actually a valid bookmark.) Differential Revision: https://phab.mercurial-scm.org/D3450