Follow-up to r1525597:

Initialize error log providers in vhosts, solving crashes
when logging from those vhosts as well as allowing a different
provider (or provider configuration) for vhosts.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1532344 13f79535-47bb-0310-9956-ffa450edef68