Add a couple of test cases.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1539846 13f79535-47bb-0310-9956-ffa450edef68
Simplify. canRead() includes an exists() check.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1539855 13f79535-47bb-0310-9956-ffa450edef68