[O] Bug: Priority-Down Sort Method Prevents Further Sorting in Daily Agenda

[Nick Daly]

First, Bastien (and everybody), thanks for all the work done on the
8.0 release.  It's wonderful, aside from the occasional bug :)

Second, that occasional bug: Priority-down (and presumably,
priority-up) in the org-agenda-sorting-strategy prevent further
sorting from occurring in the weekly/daily agenda.

For example, when sorting with the following strategies for the
weekly/daily agenda, the agenda's order is a bit screwy:

- habit-down
- time-up
- priority-down
- deadline-down
- scheduled-down
- category-keep

Unfortunately, as shown below, the default sort methods apply:
deadlines occur after the scheduled events, and we're using the
deadline-/scheduled-up sorting method instead of the correct -down
methods:

    todo:        Sched. 6x:  TODO [#A] Reply to Can't Find Directory Issue
    todo:        Scheduled:  TODO [#A] Run Search and Fix Utility
    todo:        Scheduled:  WAIT [#A] Find Entity Relationship Diagrams
    todo:         5 d. ago:  TODO [#A] Run Search and Fix Utility
    todo:        In   2 d.:  WAIT [#A] Find Entity Relationship Diagrams
    todo:        Sched.42x:  WAIT Unavailable Note List
    mail:        Sched.21x:  TODO FW: ICE DIAG
    calendar:    Sched. 4x:  Weekly Team Meeting
    todo:        Scheduled:  TODO Design Draft


The desired and correct order of the above events, based on selected
sort methods, is:

    todo:        In   2 d.:  WAIT [#A] Find Entity Relationship Diagrams
    todo:         5 d. ago:  TODO [#A] Run Search and Fix Utility
    todo:        Scheduled:  TODO [#A] Run Search and Fix Utility
    todo:        Scheduled:  WAIT [#A] Find Entity Relationship Diagrams
    todo:        Sched. 6x:  TODO [#A] Reply to Can't Find Directory Issue
    todo:        Scheduled:  TODO Design Draft
    calendar:    Sched. 4x:  Weekly Team Meeting
    mail:        Sched.21x:  TODO FW: ICE DIAG
    todo:        Sched.42x:  WAIT Unavailable Note List

Thanks for your time,
Nick