[setup] in case of Macos 10.[7, 8, 9] the value of JAVA_HOME is
overwritten (silently) and users have not chance to point to a valid
installation. Additionally the path to the headers from a recent
openjdk (1.7u51) are Home/includes instead of Home/Headers, which
is also fixed by this commit.
Merge pull request #25 from marscher/setup_java_home_ignored_on_lion

[setup] in case of Macos 10.[7, 8, 9] the value of JAVA_HOME is overwritten