[PATCH] Introduce AuthzSVNGroupsFile configuration option for mod_authz_svn

Hi,

When AuthzSVNReposRelativeAccessFile directive is being used and
authorization rules are stored per-repository, it is usually required to
have a single set of groups for all repositories.

In other words, there can be a 'developers' group, whose members should
have access to all repositories. To avoid the duplication of the 'developers'
group definition across multiple authz files, it would be great to have a
single place to define these groups.

The attached patch adds the 'AuthzSVNGroupsFile' option to specify the
dedicated file where the group definitions are stored.

Having such an option seems to be a logical step forward since we already
have the AuthzSVNReposRelativeAccessFile option. The introduced option does
not affect the existing behavior — if it is not present, everything will
remain the same.

It might seem that the patch is pretty big, but the actual change is quite
local. Group definitions are just copied when the authz config is loaded.
When the 'AuthzSVNGroupsFile' option is used, it is prohibited to define
groups in the authz files.

All tests (local, svn, http) including the new ones pass.

Thanks and regards,
Evgeny Kotkov