The epoll_reactor now supports the use of regular file descriptors with
posix::stream_descriptor, provided the I/O operations on them never fail
with EAGAIN or EWOULDBLOCK. If the descriptor cannot be added to the
epoll set using epoll_ctl, and errno is EPERM (indicating an unsupported
descriptor type), then no error condition is raised. Instead, any
operation which would require a trip through the reactor will fail.
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