scmutil: make simplekeyvaluefile able to have a non-key-value first line To ease migration from files with version numbers in their first lines, we want simplekeyvaluefile to support a non-key-value first line. In this way, old versions of Mercurial will read such files, discover a newer version than the one they know how to handle and fail gracefully, rather than with exception. Shelve's shelvestate file is an example.