Merge branch 't/sched_improvements'

Merge branch 't/sched_improvements'

This topic has been cooking for a month. During this period, one
problem on BSD has been found and fixed.

	3ad5b0 Fix build on FreeBSD
	484e75 sched: Rename new_post_select back to post_select.
	74c880 sched: Kill old ->post_select variant.
	c77e19 grab client: Switch to the alternative post select method.
	38aeac client supervisor: Switch to the alternative post select method.
	e009fa client exec: Switch to the alternative post select method.
	742718 i9e: Switch to the alternative post select method.
	2e6b8f vss: Switch to the alternative post select method.
	6e83b4 stdout: Switch to the alternative post select method.
	1995ce stdin: Switch to the alternative post select method.
	88b0ec audioc: Switch to the alternative post select method.
	b210e8 afs command task: Switch to the alternative post select method.
	12f683 afs signal task: Switch to the alternative post select method.
	ccef24 server signal task: Switch to the alternative post select method.
	a6dabd server command task: Switch to the alternative post select method.
	855c53 write: Switch to the alternative post select method.
	58b74b play: Switch to the alternative post select method.
	cf4982 afh_recv:  Switch to the alternative post select method.
	4dc05b client: Switch to the alternative post select method.
	043fd6 audiod: Switch command_task to the alternative post select method.
	ce462a audiod: Switch the status task to the alternative post select method.
	a7f2d1 audiod: Switch signal task to the alternative post select method.
	ba2f65 osx writer: Switch to the alternative post select method.
	3642d2 oss writer: Switch to the alternative post select method.
	c29db3 file writer: Switch to the alternative post select method.
	36875c ao: Switch to the alternative post select method.
	3b3049 alsa: Switch to the alternative post select method.
	60b853 wmadec: Switch to the alternative post select method.
	6c8719 wav filter: Switch to the alternative post select method.
	03e915 spxdec: Switch to the alternative post select method.
	24bbc5 resample: Switch to the alternative post select method.
	4ca80f prebuffer: Switch to the alternative post select method.
	a55083 oggdec: Switch to the alternative post select method.
	806d26 mp3dec: Switch to the alternative post select method.
	7dcaf5 flacdec: Switch to the alternative post select method.
	4dc9b9 fecdec: Switch to the alternative post select method.
	f6e2cb compress: Switch to the alternative post select method.
	ac3371 amp: Switch to the alternative post select method.
	7c2c68 aacdec: Switch to the alternative post select method.
	b333e0 dccp_recv: Switch to the alternative post select method.
	00e793 udp_recv: Switch to the alternative post select method.
	9c00a7 sched: Provide alternative post_select variant.
	24758c Replace gettimeofday() by clock_gettime().
	01f802 sched: Get rid of (pre)select shortcuts.
	5bb44a audiod: Avoid delay when closing slot.

Conflicts:
	string.c