typekit: fix include of typekit/BoostSerialization

In case rtt_scripting is supported, include the BoostSerialization header,
but do it from the correct include path.

Signed-off-by: Peter Soetens <peter@thesourceworks.com>
typegen: include string header always.

toCORBA fromCORBA for string is always generated, so include header always as well.

Signed-off-by: Peter Soetens <peter@thesourceworks.com>