Re-work EL attribute parsing. The underlying issue was complete independence of attri...

Re-work EL attribute parsing. The underlying issue was complete independence of attribute and EL parsing. The attribute parser would generate the same result - ${1+1} - after parsing ${1+1} and \${+1} and the EL had no way to differentiate between the first (that should be treated as an expression) and the second (that should be treated as a literal). The attribute parser has been modified to output any literals that would be mi-interpreted by the EL parser as EL literals. ie \ is output as ${'\\'} or #{'\\'}, $ as ${'$'} or #{'$'} and # as ${'#'} or #{'#'}.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@897614 13f79535-47bb-0310-9956-ffa450edef68