errors: use exit code 10 for parse errors Now that `ParseError`s raised while reading the config file has been converted into `ConfigError`s, the remaining parse errors should all be "input errors" (i.e. exit code 10), according to https://www.mercurial-scm.org/wiki/ErrorCategoriesPlan. Differential Revision: https://phab.mercurial-scm.org/D9332