Following up on r1534153, fix initializing the ssl provider for server
certificates and the code that tests the platform specific handling.

The reason this wasn't detected is that in general certificates are now
accepted via the root authority, instead of per certificate.

* subversion/libsvn_subr/auth.c
  (svn_auth_get_platform_specific_client_providers): Store provider in list.

* subversion/tests/libsvn_subr/auth-test.c
  (test_platform_specific_auth_providers): Update assumption and error message.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1534184 13f79535-47bb-0310-9956-ffa450edef68