c55795d055
descriptor array, which may have blocked. Change callers of fdalloc() to restart whatever they\'re doing if this condition happens. (XXX unp_externalize() needs some work, but that will be tackled later.) Change finishdup() to close the descriptor in the `new\' slot if one exists, and change sys_dup2() accordingly. Closes a race condition when using kernel-assisted user threads. While here, garbage-collect UF_MAPPED -- it is not used anywhere.