Added t5078 - make sure ^o^ won't skip commands if we're removed from a group.

When a command is removed from a group, we need to run dependent commands to check for proper dependencies even if the command's outputs are the same.
Added t5079 - make sure groups are modified with ^o^ if outputs change.

Here we remove an output from a group, so we need to make sure that the group is marked as modify so that dependent commands are executed even if the remaining outputs are unchanged.
Added t5080 - make sure transitive deps aren't broken by ^o^.

In this case, we have a normal link on a file because of a transitive dependency. When that transitive dep is broken and our output is the same, we still need to run the dependent command so that its dependencies can be checked.
Helgrind doesn't seem to like bitfields.