Checks to see that stencil commands have the correct number of arguments. (issue 5649054)

[dak]

http://codereview.appspot.com/5649054/diff/1/lily/stencil-expression.cc
File lily/stencil-expression.cc (right):

http://codereview.appspot.com/5649054/diff/1/lily/stencil-expression.cc#newcode31
lily/stencil-expression.cc:31: nargs = scm_permanent_object (scm_cons
(scm_cons (ly_symbol2scm ("dummy"), SCM_EOL), SCM_EOL));
dummy?

The whole stuff is totally incomprehensible.  It is not clear what is
stored where and for what reason, and there is no documentation
whatsoever.  It was bad before, agreed, but it has become much worse.

http://codereview.appspot.com/5649054/