anchor.diff:  configuration is to be the default if nothing is specified when Tundra is run
   on Mac OS X:
   
  +[source,lua]
   -------------------------------------------------------------------------------
   Build {
       Units = function()
  -        Program {
  +        local hello = Program {
               Name = "HelloWorld",
               Sources = { "hello.c" },
           }
  -        Default "HelloWorld"
  +        Default(hello)
       end,
       Configs = {
           Config {
  
positive.code: Tundra knows about this additional output file.
  
  <<<
  
  == The Environment ==
  
  
negative.code: property in the +Build+ block.
  
  .Config Tools Synopsis
  [source,lua]
  -------------------------------------------------------------------------------
  Tools = {
      "foo",
  