fs_io_thr loop is not waiting for timeout

[sylgal]

There is a missing mutex_lock/unlock enclosing fs_pthread_cond_timedwait.
On FreeBSD (at least) it return [EPERM] and never wait for timeout.

Here is the patch to correct this issue:

--- fstrm/fstrm.c.orig 2014-09-19 16:42:26.000000000 +0200
+++ fstrm/fstrm.c 2014-09-19 17:01:14.000000000 +0200
@@ -634,9 +634,11 @@
if (count != 0)
continue;

•            pthread_mutex_lock(&io->cv_lock);
          res = fs_pthread_cond_timedwait(io->clkid_pthread,
                                        &io->cv, &io->cv_lock,
                                        io->opt.flush_timeout);
  

•            pthread_mutex_unlock(&io->cv_lock);
          if (res == ETIMEDOUT)
                  fs_io_flush_output(io);
  }