PROTON-194: Introduce CMakeLists.txt at the top level. modified FindJava to work properly on cmake 2.6, allowing us to remove some workarounds from other cmake files

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/branches/jni-binding@1439419 13f79535-47bb-0310-9956-ffa450edef68