Add support for DVB-T2 in the same way as DVB-S2.  If the mod_sys
field of dtv_multiplex contains "DVB-T2" a DVB-T/T2 tuner will be
switched in DVB-T2 mode.  Currently there is no UI to set this so
it must be manually set in the database.
Remove "if (true ||" added during development.  This should have been removed before committing.
Support for DVB-T2 in the channel scanner.  When used with a card that supports DVB-T2
it adds the ability to select DVB-T/T2 when editing a transport and extends the full
scan to check whether a frequency will lock with DVB-T2.  It only tests for DVB-T2 if it
has failed to lock with DVB-T to avoid having duplicate entries with cards that auto-switch
between DVB-T and DVB-T2.  It also fixes a bug where previously if a lock was obtained
with an offset frequency but not with the centre frequency the entry in the database
contained only the centre frequency.