[mythtv] #5964 - SRC update

[foo bar]

#5964 was closed because I said I was going to upload an improved SSE2
implementation. I've given up on that for now - the performance
increase isn't worth the effort for the time being at least. However,
the SRC update patch (which was too big to attach, link on ticket) can
be applied. It's huge because it replaces the coefficients for the
SINC based converters and greatly improve the SNR of each. Whilst
there's not much point applying until #5900 is applied (since the SRC
is never used at the moment) could it be reopened pls?