revlog: raise an exception earlier if an entry is too large (issue4675) Before we were relying on _pack to error out when trying to pass an integer that was too large for the "i" format specifier. Now we check this earlier so we can form a better error message. The error message unfortunately must exclude the filename at this level of the call stack. The problem is that this name is not available here, and the error can be triggered by a large manifest or by a large file itself. Although perhaps we could provide the name of a revlog index file (from the revlog object, instead of the revlogio object), this seems like too much leakage of internal data structures. It's not ideal already that an error message even mentions revlogs, but this does seem unavoidable here.