Add conditional logging based upon environment variable existence.

	Add conditional logging based upon environment variable existence.
	Also add RefererIgnore functionality from mod_log_referer to
	mod_log_config; mod_log_referer and mod_log_agent are now
	deprecated.  The list of envariables to check is set up as
	an array even though the current implementation (TAKE23)
	only handles one; just in case we ever want to do something
	strange like, 'env=foo,bar,!bag'.

PR:		519, 548, 1351, 1811(?), 3449

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@82819 13f79535-47bb-0310-9956-ffa450edef68