add new input filter mode AP_MODE_INIT:

allows filters such as mod_ssl to initialize a client connection
(ie handshake) before reading request data from the client.
PR:
Obtained from:
Submitted by:   dougm
Reviewed by:	wrowe


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92042 13f79535-47bb-0310-9956-ffa450edef68