GROOVY-6963: groovydoc should honour the {@docRoot} javadoc tag
minor refactor: remove some checkstyle warnings
GROOVY-6964: Build on Windows.
Building on Windows was not supported because JarJarTask does not release a file lock.
Please read http://groovy.329449.n5.nabble.com/Build-issue-with-groovy-core-master-td5719619.html for the detail.
GROOVY-6962: Fix IllegalAccessException if the target public method belongs to a package private class