Add SNMPv3 authentication and encryption support

Adds the following configuration options to support SNMPv3 authentication:
* SecurityLevel - authPriv | authNoPriv | noAuthNoPriv
* Username - username for authentication
* AuthPassphrase - passphrase for authentication
* AuthProtocol - MD5 or SHA
* PrivacyPassphrase - passphrase for encryption
* PrivacyProtocol - AES or DES
* Context - Optional authentication context
curl_json plugin: separate the cj_curl_perform in to the curl and yajl parts
curl_json plugin: support getting json from a Unix socket as well as a URL
curl_json plugin: use sstrerr for thread safety
curl_json plugin: style cleanups
Merge branch 'pr/392'
write_riemann: Add extra meta strings as attributes in notifications
write_riemann plugin: Receive acknowledge message when using TCP.

Not receiving an acknowledge message when communicating with riemann over TCP
will cause the riemann instance to eventually hang for extended periods of time
because of resource exhaustion.

Took the time to reaorganize the riemann_send function to simplify locking.
Merge remote-tracking branch 'origin/master'
Add support for 64bit netlink counters to the netlink plugin
fix typos
libcollectdclient: Implement the lcc_server_set_interface() function.

Copied from the network plugin. License changed to MIT with permission
from Max Henkel, thank you very much!
Add support for a custom user agent at compile-time

Make it possible to specify a custom user agent at compile time
and then use on all libcurl calls instead of just going with
PACKAGE_NAME/PACKAGE_VERSION
Fix handling of 127.0.0.1 instead of localhost for *sql plugins

The mysql and postgresql plugins have special handling if you
use localhost as your hostname.  Sometimes you need to use 127.0.0.1
instead and want to not have that make changes to the hostname
for the metrics.
configure.in: Move the useragent config to a more appropriate block.
Merge pull request #425 from spotify/master

write_riemann plugin: Receive acknowledge message when using TCP.
Merge pull request #417 from udoprog/udoprog/riemann

write_riemann: Add extra meta strings as attributes in notifications
Append rules/targets to existing chain.

This patch allows appending rules/targets to an existing chain instead
of overwriting it. This way, it is possible to split filter chains
definition among several files.
Rewritten condition more clearly.
Add a JMXProvider Class Loader to be able to load Provider using
getConnectorAsService from JMXConnectorFactory. The protocol remoting-jmx
using by JBOSS > 7 need that to work.