Don't use g_thread_get_initialized.

Initialize glib threads unconditionally in main() instead
of using g_thread_get_initialized in the 9p code.

Fixes a build failure on RHEL-5, which ships glib 2.12.
g_thread_get_initialized was added in 2.20.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
