Update recommendation for registration to heartbeating

The recommendation to use registration predates having good support for STOMP
1.1 heartbeats in the stomp-gem and our connectors.

Here we rework the Note that outlines what registration does for us in terms of
keeping the connection alive and fault detection, as this also applies to
protocol heartbeats, and move it to the section on connector settings.
Fix typo in connector_activemq.md
Merge pull request #230 from juniorsysadmin/activemq-connector-typo

Fix typo in connector_activemq.md
Merge pull request #229 from richardc/docs_heartbeat_not_registration

Update recommendation for registration to heartbeating
maint - consistently stub and expect symbol names
maint - relay #make_target should create correct targets for readability
MCO-443 Use a distinct reply queue per request

In very large installations we sometimes will see late discovery
responses arrive on the reply queue after the client has moved on to
expect a response to the subsequent rpc action, as the same reply
queue will be used for all requests made by that process.

Here we avoid this by introducing Client.request_sequence to keep
track of the sequence of requests sent, and use that value to create
a distinct reply queue per request, rather than per process.
Merge pull request #231 from richardc/MCO-443_per_request_reply_queue

MCO-443 Use a distinct reply queue per request
maint - increase required api version to 2.6.0

When implementing MCO-443 we added MCollective::Client.request_sequence and
made use of it in the connectors.  This commit completes this by bumping the
required mcollective api version to 2.6.0, the first version that will have
that new api.
Merge pull request #232 from richardc/connector_api_version

maint - increase required api version to 2.6.0
(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-453) Fix validator plugin load race condition

This commit fixes a race condition which occurs when validator plugins
are loaded for the first time by adding a mutex to the Validator
module.

The race condition happens when an agent thread tries to determine
whether it should load the validator plugins, determines that they have
already been loaded by looking at the last_load timestamp but the
validators are in reality still busy loading. By locking the mutex
before the call to #load_validators? we allow
PluginManager.find_and_load to finish before we try and determine if the
validators have been loaded or not.
Merge pull request #235 from ploubser/mco-453

(MCO-453) Fix validator plugin load race condition
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