Merge branch 't/fade_improvements'

Merge branch 't/fade_improvements'

Was cooking for almost a month, let's merge it.

	483d31 fade: Upgrade client command log message to loglevel NOTICE.
	49412f fade: Handle non-positive fade time gracefully.
	376456 fade: Add --loglevel option.
	dec704 fade: Generate fade.ggo from m4 template.
	0968b2 fade: Introduce --mixer-api to choose between ALSA and OSS.
	b4171b fade: Add the ALSA mixer implementation.
	46af7d fade: Switch to modular mixer API.
	702457 fade: Infrastructure for the modular mixer API.
	3a2580 fade: Abort on client command failures.
	b618da fade: Remove some unnecessary includes.
	f502e6 configure: Add fade.o to object list only if oss was detected.