Fix missing prototype and shadowing compiler warnings.

* subversion/libsvn_subr/auth.h: Include svn_auth.h.

* subversion/libsvn_subr/config_auth.c: Include auth.h.

* subversion/libsvn_subr/simple_providers.c
  (svn_auth__simple_cleanup_walk): Remove shadowing variables.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1443693 13f79535-47bb-0310-9956-ffa450edef68