stage_poly: missed a debugging print
stage_poly::setup adds --stage_poly model header

this fixes a reported crash when run on existing model without
--stage_poly (which caused gd::save_load to be called before
stage_poly::save_load)
stage_poly: use calloc_or_die_gruesomely
stage_poly: constant needs multiplier

(relevant for --oaa and other multiple-predictor reductions)
stage_poly: misc cleanup
stage_poly: handle ft_offset
stage_poly: update ec predictions after reduction
stage_poly: support update / reduction interaction

This makes it so that multiple invocations of the same example (due to
reduction) only trigger a single support update.
Merge branch 'master' into oaa_fix
Merge pull request #341 from wfenchel/oaa_fix

--oaa fix