Provide accurate position/duration/seeking with non-constant framerates.

The recordedseek and filemarkup tables are enhanced to hold timestamp
data in addition to the existing file offset data.  The millisecond
timestamps are produced by all recorders that subclass DTVRecorder, as
well as mythtranscode and mythcommflag --rebuild.  These timestamps
are relative to the start of the recording/video.

A new command is added to the myth protocol, "QUERY_RECORDER
FILL_DURATION_MAP", modeled after FILL_POSITION_MAP, to send updated
timestamp info for playback of an in-progress recording.

The timestamp markup is used during playback to give accurate position
and duration information in the OSD wherever possible, and to provide
accurate time-based seeking, such as "skip forward 30 seconds" or
"jump to the 5-minute mark".  Timestamps are linearly interpolated
from a frame's nearest neighbors in the map, and extrapolated based on
the current frame rate when the map is missing (e.g. legacy
recordings) or incomplete (e.g. in-progress recordings).  Other than
that, the frame rate is not used for seeking or duration calculations.
(With the exception of a handful of areas that still need some
attention, including seeking based on commskipmap, seeking across
program boundaries during Live TV, and the watched flag calculation.)

The cutlist continues to be taken into account for seeking and
displaying timestamps, for the most part making cutlists
indistinguishable from the result of lossless transcoding.

Note that to get the benefit of these changes for preexisting
recordings, it may be necessary to run "mythcommflag --rebuild" on
such recordings.

Bumps the ABI and protocol versions.  "make distclean" is recommended.

Fixes #10104.
Remove now useless code.

Thank to Paul Harrison for spotting it
Merge remote-tracking branch 'upstream/master'