refer to a variable in the same section (e.g. ${:foo}).

When doing variable substitution, you can use the special option,
``_buildout_section_name_`` to get the section name.  This is most handy
for getting the current section name (e.g. ${:_buildout_section_name_}.


git-svn-id: http://svn.zope.org/repos/main/zc.buildout/trunk@103234 62d5b8a3-27da-0310-9561-8e5933582275