config: move message about leading spaces in config to config.py When the config parser raises a ParseError, it uses the line that failed to parse as the error message. It doesn't currently tell the user anything about why it failed to parse. b13b99d39a46 (config: highlight parse error caused by leading spaces (issue3214), 2014-03-16) added a checked based on the error *message* having leading spaces. That has worked fine because only the config parser uses the line itself as error message (I think the revset and fileset parsers use more user-friendly proper messages). It still feels like a hack. Let's make the config parser give a useful message about leading whitespace instead. We should ideally follow up with more useful messages for other parse errors in config files. Differential Revision: https://phab.mercurial-scm.org/D9241