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 area. 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