We have supported multiple workspaces for six months now, but I forgot
to remove a note in the revset doc saying that we don't support
it. Also update the text to descibe how to refer to the working-copy
commit in another workspace.
This introduces a `connected(x)` function, which is simply the same as
`x:x`. It's occasionally useful if `x` is a long expression. It's also
useful as a building block for `root(x)` (coming soon).
It makes sense to omit either of the arguments of the `..` operator,
even though `..x` is equivalent to `:x`. `x..`, with a implied right
argument of `heads()` is more useful.
