Move 100 - Continue support to the HTTP_IN filter so that filters

Move 100 - Continue support to the HTTP_IN filter so that filters
are guaranteed to support 100 - Continue logic without any
intervention.

This requires some reshuffling of the code in http_protocol.c so
that some static declarations are available early enough in the
code so that ap_http_filter can access them.

Note that we can not read the chunk until after (possibly) sending the
100.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94668 13f79535-47bb-0310-9956-ffa450edef68