New directory for an OSX-x64 buildslave.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1638213 13f79535-47bb-0310-9956-ffa450edef68
Rename the buildbot dir to match the other names.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1638214 13f79535-47bb-0310-9956-ffa450edef68