directaccess: add mechanism to load directaccess after some other extensions directaccess needs to load after some extensions to avoid interfering with them. This patch adds a mechanism to specify what extension directaccess needs to load after.

evolve: add another test for evolve --rev This patch adds one test for three conditions not covered before: - evolve --rev on a stack with obsolete commits without successors - evolve --rev on two sets of stacks in parallel - evolve --rev on a set of stack partially solvable (because all of the commits of the stack are not specified with --rev)

evolve: add a more complex test for evolve --rev The previous tests of evolve --rev would have passed with an ordering of revs by increasing revision numbers. This patch adds a test that would fail if that was what we were doing and therefore tests the implementation better.