- grammar of // changed to move the justification inside;

- grammar of // changed to move the justification inside;
  reason: that brain damaged piece of software that is CAMLP5 does a
    lookahead and then it forgets to rollback the token (why??? is it
    a bug). As a consequence matita used to work (since it parses a
    statement at a time), but not matitac (since the lookahead destroyed
    the next command)
- core_notation.moo: \frac used to be at level 90, but this is incorrect
    during parsing and incompatible with the new syntax; \frac is now
    used only in output
- minor dead code removal here and there