lily/tuplet.cc: build fix

[Graham Percival]

Attempting to build current CVS (which I believe is the same as the 
2.7.5 release),
I encountered this:

Writing "lilypond-internals.texi"...
error: can't find description for property directionedge-height 
(backend)
make[2]: *** [out/lilypond-internals.texi] Error 1
make[1]: *** [all] Error 2
make: *** [all] Error 2


Changing "direction" to "direction " in a list of properties in 
lily/tuplet.cc
fixed it.  Patch has been committed to CVS.

Cheers,
- Graham