Backport r27381 from trunk to release-0-24-fixes

Refactor TeletextDecoder and TeletextScreen and add a new TeletextReader
class.

This follows the approach used in the other subtitle and caption classes
whereby the screen object handles OSD representation of the data, the
reader object holds the state and data and the decoder object feeds new
data into the reader.

This simplifies setup and initialisation of the teletext objects and
removes the requirement to lock the OSD from the decoder, which was
causing endless problems.

The previous behaviour of always decoding teletext packets is also
reinstated which radically improves responsiveness. Actually decoding
and parsing the packets is trivial for a modern processor and hence
should have no impact on performance.

Closes #9271

Re-enable MythMusic -
TagLib 1.6 or later required, for PopularimeterFrame, after [27319]

Add a new StreamingRingBuffer class.

This is a new RingBuffer subclass that utilises ffmpeg's internal
streaming functionality to handle network file transfers using various
standards.

Only http is currently detected though others such as rtp, rtmp, udp etc
should in theory work - but I had no success in testing.

http seems to work without issue (but don't expect any seeking) either
via direct download or 'streamed'.

To test, try mythavtest http://myserver/myfile

Refactor the RingBuffer classes.

-- make distclean STRONGLY recommended --

This creates a proper class hierarchy for the RingBuffer classes, adds a
new FileRingBuffer class and removes the capitalisation from the file
names.

As noted in #9287, this a straight refactor with no attempt made to
optimise the interface or minimise code duplication.

Tested on 3 different boxes here with no apparent regressions.

Refs #9287

Backport 27409 from trunk

Prevent rebase tool from duplicating the libraries that it rebases,
by getting it to process only the real libs, not symlinks to them.
Thanks to Craig Treleaven for discovering/troubleshooting. Closes #9291

Fix a segfault when committing playcount/rating in mythmusic. The playback code changed a little between the original ratings patch and committal, seems under some unknown scenario we're tearing down the decoder before 'stopDecoder' is run which triggered a null-pointer segfault.

Backport [27404] to 0.24-fixes. Add missing menu titles to Metallurgy. Patch by kenni. Refs #9203.

Add --logfile support to mythtv-setup. Patch from Nick Morrot. Closes #6945

Remove a couple of redundant isNull() calls. isEmpty() returns true for null strings and strings are initialised to empty not null anyway. Patch by Ben Dailey. I've omitted the other changes in that patch, one was not as straightforward as it seems and the others were all in xmlparse.cpp which is deprecated code due for removal in 0.25. Closes #9054