a global function called approximate_distance_function() which performs the main optimization.  The
reduced_decision_function_trainer2 now depends on this global function.  This changes makes this
function optimizer available for other purposes besides use in the reduced_decision_function_trainer2
object.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%404125