Add "lowest priority first" auto-expire policy

[Robert Tsai <rtsai1111>]

Currently, the only auto-expire policies are "none" and "oldest show first".

This patch adds a new "lowest priority first" policy that orders by recpriority (from the schedule's recpriority value) before ordering by starttime.

I'm not 100% confident in my LEFT JOINs, but they appear to be doing the right thing, according to "mythbackend --printexpire" .

[Robert Tsai <rtsai1111>]

Oops. I just re-read the thread discussing this topic:

​http://www.gossamer-threads.com/lists/mythtv/users/135759

I did not implement the suggestion to copy over the recpriority from record to recorded. This means that one-time recordings will be given a default recpriority of 0 (due to the LEFT JOIN), which means they will be auto-expired first (even if the one-time recording was originally scheduled with a high priority).

I will work on that later.

[Robert Tsai <rtsai>]

This second patch implements copying of the recpriority value from the "record" table to the "recorded" table, so that recpriority is preserved for one-time recordings.

[Robert Tsai <rtsai1111>]

This last (final) patch (#3) adds recpriority information to the output of "mythbackend --printexpire".

[Robert Tsai <rtsai1111>]

Latest diff is updated against SVN#7004 for dbcheck.cpp

[danielk]

(In [7223]) Closes #171.

Adds a new autoexpire policy.

It sorts by priority then age so that lower priority shows are deleted first.

This updates the DB schema and I recommend anyone with a remote backends upgrade them at the same time if they want this functionality in the future. If you don't any new recordings on the remote backend will be considered to have the default priority for the new auto-expire method.

[cpinkham]

(In [7234]) Patch by Robert Tsai to update recpriority on recorded programs when the recpriority on the Scheduled Recording for that program is changed. References #171, Closes #311.

[cpinkham]

(In [7756]) Apply the rest of Robert Tsai's "Update metadata of recorded programs when adjusting recording schedules" patch. This updates the recpriority, recgroup, transcoder, and timestretch values on recorded programs when their corresponding scheduled recording entry is updated.

References #171, Closes #311.