The "get resource" functionality is no longer a hook. Instead, providers

register themselves by name with mod_dav. The user configures a particular
provider for a location/directory. mod_dav looks up that provider and uses
it explicitly. (the prior behavior simply asked "anybody" to satisfy the
get_resource, but it did not mesh well with user-specified providers)

*) add providers.c to deal with provider registration
*) rejigger mod_dav.c to toss the hook and use the provider
*) clean out dav/fs/ of the old scheme and have it register itself


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86195 13f79535-47bb-0310-9956-ffa450edef68