Add the core AddVersionComponent and AddVersionPlatform directives,
	which make the SERVER_SUBVERSION functionality a runtime thing and
	allow adding OS identity to the Server-Version string respectively.

PR:		2056
Reviewed by:	Jim Jagielski, Martin Kraemer, Brian Behlendorf


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@81175 13f79535-47bb-0310-9956-ffa450edef68