BUGFIX: Fix compilation on systems with EPOLLRDHUP undefined.

Since epolltable-internal.h uses this define, it must be defined before that is included.
Merge pull request #97 from JoakimSoderberg/openwrt_fixes

BUGFIX: Fix compilation on systems with EPOLLRDHUP undefined.
Do not offer EV_FEATURE_EARLY_CLOSE if we have no EPOLLRDHUP