* cygheap.cc (cmalloc): Only emit system_printf warnings on failure if
DEBUGGING.
(crealloc): Ditto.
(ccalloc): Ditto.
* dtable.cc (build_fh_name): Treat NULL return from cnew as indicative of
EMFILE condition.
(build_fh_dev): Ditto.
(dtable::dup_worker): Handle NULL return from build_fh_pc.
(dtable::vfork_child_dup): Trust dup_worker to set errno.
* fhandler.h (fhandler_base::new): Mark as nothrow.
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