stack: use self._revs in stack.heads() No code cares about the ordering of the heads anyway, so let's use the unordered property that doesn't need to be sliced (because it doesn't include base).

pick: Add a test to check that pick pick the right content

WIP on handling stacks

test: add a test for current behavior of precursors revset The precursors revset currently returns the closest predecessors of a revset. If these predecessors are not known locally, it returns an empty list.