Add new ap_list_provider_groups() API for mod_info

* Add extern "C" linkage to several headers to make it easier to use them in C++ code. PR: 42286 Submitted by: Davi Arnaut <davi haxent.com.br> Reviewed by: rpluem

update license header text

Update the copyright year in all .c, .h and .xml files

New provider function, ap_list_provider_names(), which lists all available registered providers for a specified group and version number. Visible change so add CHANGES entry.

Doxygen fixup / cleanup submited by: Neale Ranns neale ranns.org reviewed by: Ian Holsman

Update copyright year to 2005 and standardize on current copyright owner line.

fix name of The Apache Software Foundation

fix copyright dates according to the first check in

apply Apache License, Version 2.0

update license to 2004.

finished that boring job: update license to 2003. Happy New Year! ;-))

Per Greg's request, add a version string component to the ap_provider.h functions. This allows modules to register different versions of the same provider.

Fix typo in doxygen comment

Add ap_register_provider and ap_lookup_provider functions which resolve the DSO link problems for DAV and the new aaa modules by moving the provider code into the core of the server and generalizing them to be used by any code. Remove the auth{nz}_*_provider functions as they are no longer needed. Change the dav_*_provider functions to wrap the ap_*_provider functions as they have a bit more of a historical precedent that we should keep around. Reviewed by: John K. Sterling <john@sterls.com> (in concept)