Let \alterBroken tweak ties again (issue 319160043 by address@hidden)

[david . nalesnik]

Reviewers: ,

Message:
Please review.  Thanks!

Description:
Let \alterBroken tweak ties again

When tweaking Tie grobs, the music function \alterBroken has
incorrectly rejected them since 2.17.6 as not being spanners.
The method of spanner recognition is at fault: 'span-direction
is not used by TieEvent.

Please review this at https://codereview.appspot.com/319160043/

Affected files (+2, -1 lines):
  M ly/music-functions-init.ly


Index: ly/music-functions-init.ly
diff --git a/ly/music-functions-init.ly b/ly/music-functions-init.ly
index  
1f94319bce743ca1e6994eebdff7daa672db0e12..901c7429129e5a2de4b5d27ac94a41da64a4a9a2  
100644
--- a/ly/music-functions-init.ly
+++ b/ly/music-functions-init.ly
@@ -104,7 +104,8 @@ a starting spanner event, or a symbol list in the form
 form of a spanner event, @var{property} may also have the form
 @samp{Grob.property} for specifying a directed tweak.")
   (if (ly:music? item)
-      (if (eq? (ly:music-property item 'span-direction) START)
+      (if (or (eq? (ly:music-property item 'span-direction) START)
+              (music-is-of-type? item 'tie-event))
           (tweak property (value-for-spanner-piece arg) item)
           (begin
             (ly:music-warning item (_ "not a spanner"))