cmdutil.walkchangerevs: use '-1:0' instead ot 'tip:0' This avoids a possibly expensive tag lookup.

revlog.revision: avoid opening the datafile without need. If there's no inline data, revlog.revision opens the data file every time it's called. This is useful if we're going to call chunk many times, but, if we're going to call it only once, it's better to let chunk open the file - if we're lucky, all the data we're going to need is already cached and we won't need to even look at the file.

convert: document splicemap, allow setting of multiple parents

merge backout