mod_crypto: improve error message with older APRs

When compiling against APR < 1.6, the actual error message was buried in
unknown type errors from mod_crypto.h. Don't include that file at all if
we're going to error out anyway.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1781146 13f79535-47bb-0310-9956-ffa450edef68