code deduplication
costs.size() in LDF subexamples is always 1 (except for the headers: "shared" and "label")
deleting relic code

make_single_prediction is now called only from do_actual_learning_oaa and do_actual_learning_wap
It should not be called on LDF headers.
(At least, I don't see any reason for the deleted code.)
costs.size() in LDF subexamples is always 1

so we can delete the extra for-cycles
simplifying the code

do_actual_learning_oaa and do_actual_learning_wap had a lot of common code
make_single_prediction can be also much simpler
indentation
resolving some todos

example->done does not exist anymore
I am not sure whether ec->partial_prediction should be restored (after base learner learns ec) or not: OAA does it, but WAP not.
name "l" was ambiguous

ldf type renamed to "data"
example.l (polylabel type) is left (I cannot change it)
Trying to fix library/ezexample_predict failing test 59

It seems that it needs one extra call to make_single_prediction, but I don't know why.
Even better solution of failing test 59 with library/ezexample_predict

singleline mode does not call do_actual_learning(), so make_single_prediction() must be called directly from predict_or_learn()
Merge pull request #464 from martinpopel/ldf

Simplification of the ldf code