(MCO-445) Remove saucy from build defaults

This commit removes saucy from build_defaults. It went EOL July 17,
2014.
(maint) Update build defaults

This removes sid and unstable from build_defaults because we no longer
support it.
Merge pull request #233 from clantant/MCO-445/stable/saucy

(MCO-445 & maint) update build defaults
Merge branch 'stable'

Conflicts:
	ext/build_defaults.yaml
MCO-429 update changelog and releasenotes for 2.6.0
MCO-429 Add documentation of SIGWINCH to daemon reference
MCO-429 Add references to activate_agents to docs
MCO-429 add registration_splay to docs
MCO-429 add client.cfg discovery_timeout to docs
MCO-429 add soft_shutdown_timeout to docs