urlutil: provide some information about "bad url" when processing `pushurl`
It appears pushurl only support `<proto>://` entries. This is not obvious and
can lead to obscure error. We make the error less obscure as a start..
Differential Revision: https://phab.mercurial-scm.org/D10455
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true