RSP's header directives shall be generated before handling ETAG and Last-Modified

[tomyeh]

Thus, the headers will be generated even under 304.

Note: the header directives ([:header]) must be specified before any other tags except [:page] and [:header]. Otherwise, it won't be generated under 304.

For example, in the following code, foo1 will be always generated, while foo2 will be generated only if 200.

[:page etag="true"]
[:header foo1="abc"]
[:dart][/dart]
[:header foo2="abc"]

[tomyeh]

baa51d6