BUG/MEDIUM: http: 100-continue responses must process the next part immediately

BUG/MEDIUM: http: 100-continue responses must process the next part immediately

Since commit d7ad9f5 ("MAJOR: channel: add a new flag CF_WAKE_WRITE to
notify the task of writes"), we got another bug with 100-continue responses.
If the final response comes in the same packet as the 100, then the rest of
the buffer is not processed since there is no wake-up event.

In fact the change above uncoverred the real culprit which is more
likely session.c which should detect that an earlier analyser was set
and should loop back to it.

A cleaner fix would be better, but setting the flag works fine.
This issue was introduced in 1.5-dev22, no backport is needed.