write_http plugin: Remove custom string and boolean config handlers.
increased buffer size
Fix link to memcached protocol
Submit listen_disabled_num in memcached.c

This is a counter which increments when the connection limit to
memcached is reached and a socket listen is disabled.
Remove _num suffix from listen_disabled_num collected value
Syslog: if we can't find the loglevel specified by the configuration string default to 'info' and warn about the unknown configuration option. no way to make syslog totaly silent anymore.
Add support for durable AMQP queues

The collectd amqp plugin allows setting messages as persistent but is hardcoded to create or use transient queues that are set to auto_delete.  This commit adds support for QueueDurable and QueueAutoDelete boolean values in the config file and changes the queue creation as appropriate.

If the values are not set in the config file, QueueDurable defaults to false and QueueAutoDelete defaults to true.

Tested with RabbitMQ 3.3.1
Merge pull request #636 from dothebart/config_debug_nonsilent

Syslog: don't go all silent on 'debug' with production binary
add brackets to the list of characters graphite chokes on

(cherry-pick of 109cc80a to avoid a merge conflict later on)
mention new options to cpu plugin in example config
remove quotes in example config to make all statements consistent
Merge pull request #619 from Crapworks/master

increased buffer size