BUG/MINOR: http-ana: Don't switch message to DATA when waiting for payload

BUG/MINOR: http-ana: Don't switch message to DATA when waiting for payload

The HTTP message must remains in BODY state during the analysis, to be able
to report accurate termination state in logs. It is also important to know
the HTTP analysis is still in progress. Thus, when we are waiting for the
message payload, the message is no longer switch to DATA state. This was
used to not process "Expect: " header at each evaluation. But thanks to the
previous patch, it is no long necessary.

This patch also fixes a bug in the lua filter api. Some functions must be
called during the message analysis and not during the payload forwarding. It
is not valid to try to manipulate headers during the forward stage because
headers are already forwarded. We rely on the message state to detect
errors. So the api was unusable if a "wait-for-body" action was used.

This patch shoud fix the issue #2093. It relies on the commit:

  * MINOR: http-ana: Add a HTTP_MSGF flag to state the Expect header was checked

Both must be backported as far as 2.5.