Separate default devices for playback and capture

["Lasse Kärkkäinen" <tronic+8nhy@trn.iki.fi>]

I've been reading the library source code and from what I gather, it
seems that it just fundamentally cannot support separate config sections
for playback and capture.

What should the fix be? I can see three options:

1. allow specifying in asound.conf whether a section is for recording or
playback (needs major redesign of conf.c and some changes in pcm.c).

2. if the name is "default", use "capture" (for example) instead, in
snd_pcm_open_noupdate, maybe reverting to "default" if the other device
cannot be found (dirty, but very easy to implement)

3. tell application developers to use some other device name for
capture: "capture", instead of "default", for example (needs a little
change in every application program that uses ALSA capture).