* input/regression/beam-quant-standard.ly: reindent, set

* input/regression/beam-quant-standard.ly: reindent, set
debug-beam-quanting to #t.

* lily/beam-concave.cc (calc_concaveness): set concaveness to
10000 if this is a "hard" concave beam.

* lily/beam.cc (calc_least_squares_positions): change from
calc_least_squares_dy
(set_stem_lengths): this is now a chained callback.

* lily/context-property.cc (execute_general_pushpop_property):
bugfix override with procedure should have effect.

* scm/define-grob-properties.scm (all-internal-grob-properties):
remove position-callbacks.

* scm/define-grobs.scm (all-grob-descriptions): use
ly:make-callback-chain for positions property.

* scm/layout-beam.scm (check-quant-callbacks): return list of
chained callbacks.

* scm/lily.scm (type-p-name-alist): add callback-chain

* lily/lily-guile.cc (type_check_assignment): type check failure
is warning not message.

* lily/grob-property.cc (try_callback): walk callback chain if
appropriate.

* lily/chained-callback.cc: new file. new smob type.

* lily/lily-guile.cc (procedure_arity): new function.