BUG/MINOR: http-ana: Reset response flags when 1xx messages are handled

BUG/MINOR: http-ana: Reset response flags when 1xx messages are handled

Otherwise, the following final response could inherit of some of these
flags. For instance, because informational responses have no body, the flag
HTTP_MSGF_BODYLESS is set for 1xx messages. If it is not reset, this flag will
be kept for the final response.

One of visible effect of this bug concerns the HTTP compression. When the final
response is preceded by an 1xx message, the compression is not performed. This
was reported in github issue #229.

This patch must be backported to 2.0 and 1.9. Note that the file http_ana.c does
not exist for these branches, the patch must be applied on proto_htx.c instead.