Changes to mod_log_config to allow naming of format strings.

	Format nicknames are defined with "LogFormat fmt nickname", and can
	be used with "LogFormat nickname" and "CustomLog logtarget nickname".


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@79202 13f79535-47bb-0310-9956-ffa450edef68