UNSET the VirtualHost's LogLevel just before calling ap_merge_log_config(),

UNSET the VirtualHost's LogLevel just before calling ap_merge_log_config(),
to make sure that the DEFAULT_LOGLEVEL (APLOG_WARNING) is also in effect
when ap_process_config_tree() in main.c:main() walks through the
VirtualHost sections.

See https://mail-archives.apache.org/mod_mbox/httpd-dev/201404.mbox/%3C535CC85B.80501%40velox.ch%3E
for one case this is addressing. This reverts the change from r1024427 on
the one hand, but still ensures correct LogLevel merging on the other hand.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1672014 13f79535-47bb-0310-9956-ffa450edef68