Allow for Aliases at the resource level.

Allow for Aliases at the resource level.

This is to prevent situations of relying on symlinks, or Filters
while still make outside directories appear as part of the webapp.
(A common feature request seen on the user list)

Example usage:
<Context ... >
  <Resources className="org.apache.naming.resources.FileDirContext"
               aliases="/doh/=C:/tmp/woohoo/,
                        /mmmmmm/=C:/opt/data/doughnuts/" />
</Context>

If the feature is NOT used - there is no additional overhead.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc6.0.x/trunk@575332 13f79535-47bb-0310-9956-ffa450edef68