D4041: revisions: allow "x123" to refer to nodeid prefix "123"

[Yuya Nishihara]

>   Note that we attempt to resolve symbols as nodeid prefixes after we've
>   exhausted all other posibilities, so this is a backwards compatible
>   change (only queries that would previously fail may now succeed).
>   
>   I've still hidden this feature behind an experiemntal config option so
>   we can roll it back if needed.

I guess nobody would love this syntax, but I have no alternative idea.
Queued this as it is an experimental feature.