QPID-5890: Refactoring AclModule.h
* make single instances of strings associated with enums
* make more compact search functions
* make string definitions const
* return 'const string&' instead of copies of temporaries
* add self test as string defs sanity check
* export AclHelper to satisfy tests (!!)



git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1609828 13f79535-47bb-0310-9956-ffa450edef68