[vdr] xmltv2vdr speedup and modification

Hi,

I recently worked on xmltv2vdr.pl (version 1.0.6) and checked why it was so slow on my mighty Celeron 233. So I modified it a little to avoid reading all the xmltv file for each channel defined in the channels.conf. The result is good : I can process my 5Mo xmltv file in less than 10 minutes whereas it took at least 1 hour with vanilla 1.0.6 release.

I also added support for sub-title in the xmltv file (I think someone already posted about that in the list).

I only use it for one week so it can still be buggy. I'll be happy to take care of any bug found.

Hope this helps those with old hardware like me.

Sebastien