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'
Merge remote-tracking branch 'origin/master'
collectdctl: Add the "show" command.

The show command can be used to do SQL-like queries against the current
values stored within the daemon.
unixsock plugin: Add filtering regexen to the LISTVAL command.
collectdctl: Base the "show" implementation on the new LISTVAL syntax.

Pass the selector on to collectd to have it filter the values it
returns. Presumably this is much more efficient than filtering
in the client (i.e. collectdctl).
libcollectdclient: Implement the lcc_listval_with_selection() function.

This function exports the new selection feature of the LISTVAL command
with a straight forward C API. The existing lcc_listval() function
remains for backwards compatibility (and ease of use) and will
internally use the new and more complex function.