Add exactFind() method.
Use it to simplify one of Mapper methods, addWrapper.
Fixed error logging there. Old behaviour was to log only "(pos<0)" case. It did not log in wrong-match-found case (wrong name).

This backports part of r1604066.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1604677 13f79535-47bb-0310-9956-ffa450edef68
Simplify removeWrapper.
This backports part of r1604066.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1604680 13f79535-47bb-0310-9956-ffa450edef68
Simplify addWelcomeFile, removeWelcomeFile, clearWelcomeFiles.
This backports part of r1604066.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1604683 13f79535-47bb-0310-9956-ffa450edef68