* lily/smobs.cc (protect_smob): switch off fancy smob protection

* lily/smobs.cc (protect_smob): switch off fancy smob protection
for now.

* lily/include/performer.hh (class Performer): strip get_tempo() method.

* lily/midi-def.cc: strip file.

* lily/lexer.ll (Lily_lexer): don't protect hash key separately.

* lily/include/context-def.hh (struct Context_def): use
VIRTUAL_COPY_CONSTRUCTOR().

* lily/source-file.cc: smobification.

* lily/include/source-file.hh (class Source_file): smobify
Source_file. Trim redundant members.

* lily/parser.yy (Lily_lexer::try_special_identifiers): unprotect
clones after creation. This plugs a huge memory leak.

* python/convertrules.py (FatalConversionError.sub_tempo):
complete rule for \midi{ \tempo }

* input/mutopia/J.S.Bach/wtk1-fugue2.ly (bassdux): idem.

* input/mutopia/F.Schubert/morgenlied.ly (pianoLH): update tempo.