Finish dup logic for open files; fix bug in sigtimedwait(), would return wrong...

Finish dup logic for open files; fix bug in sigtimedwait(), would return wrong signo value if the signal was already pending

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5517 42af7a65-404d-4744-a932-0658087f49c3