* lily/grob.cc (pure_relative_y_coordinate)

* lily/grob.cc (pure_relative_y_coordinate)
(pure_height): use the new call_pure_function stuff

* lily/grob-property.cc (call_pure_function): wrapper for the scheme
call-pure-function

* lily/side-position-interface.cc (pure_y_aligned_side): add an
optarg

* lily/simple-closure.cc (ly_eval_simple_closure): make
simple-closure evaluatable from scheme
(evaluate_with_simple_closure): make simple-closures pure-
evaluatable

* lily/slur.cc (pure_outside_slur_callback): new function

* ly/paper-defaults.ly: change default blank-page-force to 2 (this
fits in with previous changes that made the page forces much
smaller)

* scm/define-grobs.scm (call-pure-function): generalise pure-Y-offset
and pure-Y-extent into this new function.
(pure-conversions-alist): add outside-slur-callback