changegroupsubset(): ancestors() is not inclusive, we need to remove the "heads"

changegroupsubset(): move comment at the right place

changegroupsubset(): refactor the prune() functions

Merge with stable

help: make helptable a list instead of a tuple The table should always have been a list so that extensions can append their own help topics -- hgsubversion would like to do this now.

test-command-template: test 'children' template keyword

templates: 'children' keyword The template keyword 'parents' is already present and this just provides the complimentary template keyword.

changegroupsubset(): change variable names, simplify lookup logic

changegroup(): used "linkrev" instead of "revlink"

fix comment