making QUIET_BUILD the default

[Werner LEMBERG]

Is there a particular reason to no making `QUIET_BUILD' the default?
For Metafont, it's extremely chatty otherwise...

On the other hand, I suggest to change

  ifdef QUIET_BUILD
  LILYPOND_BOOK_WARN = --loglevel=NONE
  else
  LILYPOND_BOOK_WARN = --loglevel=WARN
  endif

to

  ifdef QUIET_BUILD
  LILYPOND_BOOK_WARN = --loglevel=ERROR
  else
  LILYPOND_BOOK_WARN = --loglevel=WARN
  endif

in file `make/lilypond-vars.make' to still have fatal errors sent to
stderr.


    Werner