context: follow all branches in blockdescendants()...
context: follow all branches in blockdescendants()
In the initial implementation of blockdescendants (and thus followlines(...,
descend=True) revset), only the first branch encountered in descending
direction was followed.
Update the algorithm so that all children of a revision ('x' in code) are
considered. Accordingly, we need to prevent a child revision to be yielded
multiple times when it gets visited through different path, so we skip 'i'
when this occurs. Finally, since we now consider all parents of a possible
child touching a given line range, we take care of yielding the child if it
has a diff in specified line range with at least one of its parent (same logic
as blockancestors()).
