[mythtv] Reducing frontend startup time

[Lawrence Rust]

Hi all,

I've put together 5 patches on the devel/lvr/startup branch which
together considerably reduce the startup time on remote frontends.  The
saving is especially significant on my Raspberry Pi's where the time is
reduced from around 15 seconds down to 5.

The changes mainly introduce static caches around MySQL select
operations that retrieve static settings.  I've also included a patch to
UPnP startup to make the UPnP announcement run in it's own thread and so
not delay the main thread - this saves a second or so.

I've been using these patches on my own systems for a couple of years
now.  But before I pushed I wanted to give everyone a chance to comment
on them as they have a significant impact on the database.  

Thanks.

-- 
Lawrence Rust