* lily/global-context.cc (run_iterator_on_me): fix grace note

nesting by initting measurePosition.

* lily/timing-translator.cc (initialize): do no init
measurePosition

* lily/include/music-output-def.hh (class Music_output_def): add
input_origin_ field.

* Documentation/user/changing-defaults.itely (Changing context
properties on the fly): new node.

* lily/include/ly-smobs.icc (free_smob): remove smobbed_self()
function. Only have smobbed_copy (), and do not provide
smobbed_copy() for non-simple smobs. Changes throughout.