Backport r1133152, r1133158:

Fix segfault and log proper error message if apr DBM driver cannot be loaded.

PR: 51751
Reviewed by: sf, trawick, rpluem


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1165381 13f79535-47bb-0310-9956-ffa450edef68