Moved exclusion logic to a higher level so that printf output is more readable when the same stdout FILE* is shared
by many pthreads (tasks did not have this probablem because they have separate stdout streams).


git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@174 42af7a65-404d-4744-a932-0658087f49c3