Stem direction with ties

[Per Starbäck]

With

\version "2.16.2"

\relative c'' {
  b~ b8 a b4~ b8 c
  a8 b~ b4 c8 b~ b4
}

the stems of every b goes downwards. I think it would be better if tied
notes had the same direction, to make it clearer visually that they belong
together. Then two of these stems should go up instead.

With beams it does work like that. Shouldn't ties be even more so than
beams? I have no references saying that it should be so, but here is the
actual example where I encountered it:

  b4~(-> b8. g16 \times 2/3 { fis8 e dis) }

This is RH 3rd measure of Carl Nielsen's Alfedans, and has the b-stem up in
the original.

(That original also has the b-stem up in the following measure

  cisis4.( dis8 b')\staccato r

though. Maybe it treats even slurs as a reason to get the same direction
when it's a b that is in the middle anyhow.)