Add IRC freqtable to per-video-source setting

[sphery <mtdean@…>]

The IRC frequency table was never added as a selection for the per-video-source frequency table setting. The attached trivial patch adds it.

[sphery <mtdean@…>]

Although I had convinced myself that doing so was a waste of time because of the near-zero chance of adding a new analog frequency table in the future, I considered changing the approach used to populate the "Channel frequency table" comboboxes. Currently, we're specifying the list of frequency tables in 3 places (in the chanlists[] in frequencies.c and in comboboxes in videosource.cpp and backendsettings.cpp). I don't know if there's any particular reason for keeping all three lists, but it seems that using the names from chanlists[] to populate the comboboxes would prevent a similar discontinuity in the future.

Therefore--because I felt guilty about the "maintenance headache" I left in place--I made mythtv-frequency_table_comboboxes.patch, which changes the comboboxes in videosource.cpp and backendsettings.cpp to pull their options from chanlists[] (although the one in videosource.cpp still retains the "default" setting at the top of the list). Each patch stands on its own, and mythtv-frequency_table_comboboxes.patch obviates the need for mythtv-irc_video_source_freqtable_override.patch, so you can choose the approach you prefer.

[sphery <mtdean@…>]

Different approach for populating comboboxes (fixes the original issue with a different approach)

[danielk]

(In [9684]) Closes #1653. Add IRC frequency table support in a few places.

This is another US Cable frequency table, which is offset 1.25Mhz from the HRC table.

[danielk]

(In [9685]) References #1653. Backport of IRC table selection fix in [9684].