ALSA0.5 support?

[Christian Esken]

I just have dropped ALSA 0.5 support: I added an #error statement to
mixer_alsa5.cpp

Reasons:
1) The KMix ALSA0.5 driver is the only driver that is using this troublesume 
"m_cardid" value (this is the evil variable leading to duplicated mixer 
entries).
2) ALSA0.5 is not even supported by the ALSA project anymore.

If anybody has objections, (s)he should speak up now (or hold forever 
peace :).

Chris