Issue 4545: Use Grob::programming_error in Semi_tie:: and Tie::less

[dak, 2015-08-08 17:05:40]

https://codereview.appspot.com/259210043/diff/1/lily/semi-tie.cc
File lily/semi-tie.cc (right):

https://codereview.appspot.com/259210043/diff/1/lily/semi-tie.cc#newcode102
lily/semi-tie.cc:102: return false;
This may sound facetious and your code corresponds to the previous code, but if
you return false here, you can have both a < b and b < a which may confuse some
sorting algorithms.  In the interest of causing minimal followup damage, I'd
return true for this (but not the previous) return statement.  This puts
uncastable items at a defined place in sort order (last) while not claiming a <
a (because if both items are uncastable, the first return statement will return
false already).

[Dan Eble, 2015-08-08 17:25:02]

sort non-ties last