[mythtv] Maximum visible channels in guide

[Andrew Leech]

Hi,
In my setup i've got 14 total channels, and a tv screen which is large 
enough to see them all at once in the tv guide no worries, but the c 
code (guidegrid.h & mythuiguidegrid.cpp) has a max value of 12 visible 
channels hardcoded.
New theme structure has a separate setting for maximum visible channels, 
so should be used as the defining value, without being strictly limited 
to a relatively small number by the code.

I wrote a patch to fix this some time ago and chucked it on a new 
feature ticket in trac, but it didn't get much attention there, I'm 
assuming this is a better place to discuss.
http://code.mythtv.org/trac/ticket/9578

The hard set figure does statically define the size of a couple of 
arrays, so it would be more memory efficient to dynamically create them 
based on the theme, but this was a simple way of doing it.

Cheers,
Andrew