shortened flags affair, part 8: choosing appropriate flag (issue4312057)

[lemniskata . bernoullego]

Reviewers: mike_apollinemike.com,

Message:
Hi,

here comes the main part: code that chooses flags.
I'm aware that it's quite imperfect. I'm working on it, however some
problems are perhaps beyond my skills.
Since i'll be busy after the weekend, it would be great if we were able
to discuss and polish this as quickly as possible :)
Opinions and pointers are much welcome!

cheers,
Janek

PS The exact shapes of the shortened flags are yet to be discussed. I'll
post them separately after this part is finished.

Description:
shortened flags affair, part 8: choosing appropriate flag

This is a first draft of the code that will choose appropriate flag and
attach it to stem.
feta-flags.mf has changed structure - eventually there will be many
(5-10) lengths of each flag.
I've added one shortened version of each flags; these are by no means
ultimate
(their shape will depend on 'shortening' parameter much more) and their
only purpose
is to test how c++ code works.

Please review this at http://codereview.appspot.com/4312057/

Affected files:
  M lily/stem.cc
  M mf/feta-flags.mf