obsolete: add isenabled function for option checking Previously, obsolete used the module level _enabled flag to determine whether it was on or off. We need a bit more granular control, so we'll be introducing toggle options. The isenabled() function is how you check if a particular option is enabled for the given repository. Future patches will add options such as 'createmarkers', 'allowunstable', and 'exchange' to enable various features of obsolete markers.