TabNoteHead.style = #'slash supported. (issue 53290045)

[dak]

https://codereview.appspot.com/53290045/diff/1/scm/tablature.scm
File scm/tablature.scm (right):

https://codereview.appspot.com/53290045/diff/1/scm/tablature.scm#newcode27
scm/tablature.scm:27: ((slash) "2slash"))))
This one is missing an else branch or the return value will be undefined
(which may include "2cross").  Yes, it did miss the "else" before your
change as well, but that's not an excuse.  What's called for here?  #f
or something?

https://codereview.appspot.com/53290045/diff/1/scm/tablature.scm#newcode34
scm/tablature.scm:34: (if (and (symbol? style)
That would seem to be easier to write as
(case style
  ((cross slash) (stencil-whiteout ...))
  (else (tab-note-head::print grob)))

In particular, there is no point in checking style to be a symbol before
comparing it to be eq? to a symbol: eq? comparison is a primitive
mapping to a single assembly code instruction anyway.

https://codereview.appspot.com/53290045/