clone: extract helper for checking mutually exclusive args
We have some duplicated code for aborting if the user provided
mutually exclusive arguments. Extensions surely have more such
code. We also have duplicated translations and inconsistent output in
This patch introduces a simpler helper for checking if more than one
option among a given set was given on the command line. I've made the
clone code call the function to show that it works.
The function has no good way of checking arguments with hyphens in
them. I'll add that later if necessary. The function still won't be
applicable in all cases, but I think it's still better than nothing.
Differential Revision: https://phab.mercurial-scm.org/D7633