Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56612
Correctly parse two consecutive escaped single quotes when used in UEL 
expression in a JSP.
Includes various unit tests that check the parsing of ${'\'\''}

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1601787 13f79535-47bb-0310-9956-ffa450edef68