Added code to ap_ssi_get_tag_and_value() to avoid converting

SSI tags to lowercase when they're already lowercase (in my
experience, this special case happens often enough to be
worth optimizing)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92286 13f79535-47bb-0310-9956-ffa450edef68