[vdr] sub channel numbering system

[Timothy D. Lenz]

Would it be possible to add support for the subchannel numbering system used
with ATSC? Exmple of the channels in our area:

4       KVOA
4.1    KVOAD
6       KUAT
6.1    KUATD1
6.2    KUATK
6.3    KUATV
6.4    KUATC
9       KGUN
9.1    KGUND
11     KMSB
11.1  KMSBH
13     KOLD
13.1  KOLD-DT
14     KUDF
18     KTTU
18.1  KTTUDT
27     KUAS
27.1  KUASHD
34     KFTU
38     KUVE
40     KHRR
40.1  KHRR-DT
48     K48GX
58     KWBA
58.1  KWBA-DT
58.2  LATV

All the x.x channels are the new ATSC channels, rest are old NTSC most of
which, but not all, will be shut down in a year. For ATSC .1 is the primary
channel and .2, .3, etc are the sub channels.  The "#" on the remote could
be used for the "." In the channels.conf an ATSC next channel number would
look like:
:@13.1