Added missing GLib thread initialization.

Added missing GLib thread initialization.

Older GLib versions (< 2.32, e.g. the ones shipped with CentOS 5 and 6,
SLES11, Debian 6) need an explicit initialization to make things
thread-safe, see:

  https://developer.gnome.org/glib/stable/glib-Deprecated-Thread-APIs.html#g-thread-init

RRDtools didn't do that, so you get random crashes in clients and the
rrdcached on those systems.  Now we make sure that GLib is properly
initialized before calling into it.