configure.in: perfrom variable substitution on all the

files living in extra/

Makefile.in: on "make install", create an original/
directory that will contain pristine copies of all the
config files and make adjustments to also install the
files in extra/.

Some review of this would be nice, since I hate mucking
around in the build system. 


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/simple-conf@159939 13f79535-47bb-0310-9956-ffa450edef68