Under windows, paths passed to mkpath, mkdir_p and mkdirs need to be normalized. Otherwise ruby may decide to treat the drive component as a directory (i.e. create a directory named "C:"). This patch hooks in at a low level to work around this issue.

git-svn-id: https://svn.apache.org/repos/asf/buildr/trunk@1537858 13f79535-47bb-0310-9956-ffa450edef68