base -- a boolean or a string. If it is a string, then use
          that string as a base

before, if it was a string it was never used because the expression 
"if str("something"):" is always True


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@38811 20353a03-c40f-0410-a6d1-a30d3c3de9de