Correct message that is logged when load-on-startup servlet fails to load.
It was logging context name instead of servlet name.
Also correct message key. The message belongs to StandardContext. It is not used anywhere else. It is not used by StandardWrapper.

To test: uncomment CGIServlet in conf/web.xml and look for messages in localhost.$DATE.log file.
Merged r1640672 from tomcat/tc8.0.x/trunk.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1640673 13f79535-47bb-0310-9956-ffa450edef68
Update CGI-howto.
Recommend to copy the servlet into one's own web application instead of uncommenting it globally.
The default value for cgiPathPrefix is null. The "WEB-INF/cgi" value is the recommended one and used in conf/web.xml example.

Merged r1640674 from tomcat/tc8.0.x/trunk.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1640675 13f79535-47bb-0310-9956-ffa450edef68