Bug #172812 - When a package needs to be uninstalled in advance rather

Bug #172812 - When a package needs to be uninstalled in advance rather
than through replacement, show the corresponding [blocks] entries in the
displayed list. In order to show more structure in the --tree display,
expand Package -> Uninstall edges into Package -> Blocker -> Uninstall
edges. Also, create edges between a package's own blockers and it's
Uninstall task since it's blockers become irrelevant as soon as it's
uninstalled. (trunk r9983)

svn path=/main/branches/2.1.2/; revision=9989