netcmd plugin: Added a first version of a control socket plugin.
netcmd plugin: Re-indented the entire file. Switched to "complex" config.
netcmd plugin: Some more work towards a working TLS setup.
netcmd plugin: Implemented a fgets(3)-like wrapper around gnutls_record_recv(3).
netcmd plugin: First version with working TLS.
netcmd plugin: Add work-around for GCC warning.

Change-Id: Iec6ffaf77e4ef3be90a677d3c51804affcf532cc
src/collectd.conf.in: Fix netcmd example port.

Change-Id: Ia1ae53d1dbc4052c4171404a28631607a7a4055b
netcmd plugin: Require a good TLS setup if "verify peer" is requested.

Change-Id: I0919bdade3eca33a0304c4f72033ea4734da091b
collectd.conf(5): Add documentation for the "netcmd" plugin.

Change-Id: Ibbaad0b20d9a45ca28e93add0cb53370440b3e62
configure.in: Add check for libgnutls.

Change-Id: I72094d5fe7a0f8680682ae54a17b1cf5c404f8d6
netcmd plugin: Free peers when shutting down.

Change-Id: Icfb4a988abbbd877abdfbfd137a0127be547dade
netcmd plugin: Create a "proxy" thread.

This thread is supposed to proxy data from GNU TLS to a pipe, so we can
use FILE* to access the stream. Unfortunately, this doesn't quite work
yet :(
netcmd plugin: Free the pthread attr structure.
netcmd plugin: Use boolean values where appropriate.
netcmd plugin: Use cf_util_get_service() to handle the "Port" option.
collectd.conf(5): netcmd plugin: Document how to enable TLS.