Delete package/work dir at clean task

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2637 f4f36d40-9719-0410-9868-dde021a23eda
Rewrite getting build framework locateion from literal "build/Default" to function

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2638 f4f36d40-9719-0410-9868-dde021a23eda