wix: include the help for pager Similar (I assume) to 65d2538ac993.

manifest: check 'if x is None' instead of 'if not x' The old code here would end up executing __len__ on a tree manifest to determine if 'not _data' was true or not. This was very expensive on large repos. Since this function just cares about memoization, we can just check 'if _data is None' instead and save a bunch of time.