rhg: Align with Python on some revset parsing corner cases
In particular:
* A string of ASCII digits can be either an integer on a hex prefix
* The NULL node ID should convert to the NULL revision number
Differential Revision: https://phab.mercurial-scm.org/D11409
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true