dirstate: improve error message on file/directory clash
adding helloabort: '\n' and '\r' disallowed in filenamesadding helloabort: '\n' and '\r' disallowed in filenamesadding helloabort: '\n' and '\r' disallowed in filenamesadding helloabort: '\n' and '\r' disallowed in filenamesf hello hellof hello hello