Some fixes for alsa_stream

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Hi Devin,

I've made a few fixes for your alsa_stream.c, used on tvtime.
They are at:
	http://git.linuxtv.org/xawtv3.git


In particular, those are the more interesting ones:

commit a1bb5ade5c2b09d6d6d624d18025f9e2c4398495
    alsa_stream: negotiate the frame rate

Without this patch, one of my em28xx devices doesn't work. It uses
32 k rate, while the playback minimal rate is 44.1 k.
I've changed the entire frame rate logic, to be more reliable, and to
avoid needing to do frame rate conversion, if both capture and playback
devices support the same rate.

commit 8adb3d7442b22022b9ca897b0b914962adf41270
    alsa_stream: Reduce CPU usage by putting the thread into blocking mode

This is just an optimization. I can't see why are you using a non-block
mode, as it works fine blocking.

commit c67f7aeb86c1caceb7ab30439d169356ea5b1e72
    alsa_stream.c: use mmap mode instead of the normal mode

Instead of using the normal way, this patch implements mmap mode, and change
it to be the default mode. This should also help to reduce CPU usage.

Feel free to rebase those patches and apply into your tvtime tree, if you
want.

Cheers,
Mauro.