Treat the bitwise OR of two enum values as an int.

Treat the bitwise OR of	two enum values	as an int.

This makes our interfaces usable from C++, which doesn't believe
you can say    "bufferevent_socket_nase(base, -1,
BEV_OPT_CLOSE_ON_FREE|BEV_OPT_DEFER_CALLBACKS)" but which instead
would demand "static_cast<bufferevent_options>(BEV_OPT_CLOSE_ON_FREE|
BEV_OPT_DEFER_CALLBACKS))" for the last	argument.

Diagnosis and patch from Chris Davis.

svn:r1456