Fixed option 'mac_do_not_generate_plist' declaration missing Boolean type.
Added option 'source_jvm_version' for specifying javac source version. javac does not allow target version to be lower than the source version, which by default is the level of the specific javac used. For example, when using 1.7 javac to compile to target 1.6, javac does not allow it. This new option would make this possible.