ssa.c: Add logging to g_rclose_callback
ssa.c: Push rclose to thread pool
ssa_log.c: Set flog pointer to NULL after close.
ssa_log.c: Avoid closing stderr or stdout.

 SSA may use stderr or stdout for log. If an application
 use stderr or stdout after, this will likely crash the application
 in unexpected way.
cleanup: Move ssa log closing after cleanup
ssa.c: Report in ssa_cleanup number of rsocket waiting for close.