Added SYS_INIT()

This macro simplifies calling initialization functions that must be
called only once in a multithreaded environment.
Use SYS_INIT() to initialize gfsys
sys-init: Fixed incorrect definition of sys_init_mutex
test/gfsys: Added library -lrt to Makefile.am
sys-init: Added termination support
sys-async: Fixed problems with RCU management
sys-async: Fixed multiple execution of a RCU timer
sys-calls: Minor change
sys-async: Release RCU timer when it times out