- Make lilypond locale-independent

- Fix opening files with UTF-8 characters in the file name (this also affects
  -dread-file-list) (Reported by Thomas Morley):
  $ lilypond-git filename_名字.ly
  GNU LilyPond 2.19.52
  warning: cannot find file: `filename_??????.ly'
  fatal error: failed files: "filename_??????.ly"

- /input/regression/utf-8.ly changed spacing/line.break (Reported by Thomas Morley)
  Might be related to the floating point issue below

- Investigate why the floating point numbers are different in some decimal
  digits (Reported by )

- Investigate why lilypond is a lot slower when using guile-2.0

- (display (make-simple-markup "xy"))

  results in:

  2.19.51:
  (#<procedure simple-markup (layout props str)> xy)

  2.19.52-guile2
  (#<procedure simple-markup (a b c)> xy)
  Which is technically correct but not helpful.

  Quote from David Kastrup:
    
    I don't think that we can do anything here except possibly not produce
    a procedure in the first place but rather a callable Guile structure, with
    its own print procedure consulting the documentation string (which
    contains the actual arguments these days I think since I already got
    bitten by this in the course of Guile-2 conversion and autogeneration of
    the Internals Reference: it's not like I haven't done any Guile-2
    conversion work previously).

    But that would come at some cost.  It would also make sense to remove
    the "layout props" parts of the arguments similar to "parser location"
    have been removed.

    And while one is at it, unify markups and markup lists.  And so on.


FIXED or UNRELATED:

- /input/regression/keys.ly looks bad (Reported by Thomas Morley)
  This is due to the fix for
  https://sourceforge.net/p/testlilyissues/issues/660/