dispatch: don't stack trace on commands like `hg .log`
This used to stack trace because it raised a util.Abort which wasn't
handled in this block. We now handle it. Additionally, we error out
earlier instead of plodding on and showing the "log" entry of the
plain `hg help` output.
gitweb, monoblue: port highlighting linked lines from paper
This is adapted from
41c4bdd1d585,
fbfe5748ef3e and
f3393d458bf5.