Fix a few lilypond-book bugs on windows (Issue 1815). (issue 5183042)

[reinhold . kainhofer]

http://codereview.appspot.com/5183042/diff/1/python/book_snippets.py
File python/book_snippets.py (right):

http://codereview.appspot.com/5183042/diff/1/python/book_snippets.py#newcode643
python/book_snippets.py:643: os.rename (src, dst)
Doesn't this REMOVE the src?
os.link creates a link at dst, so the files at src and dst are actually
the same file (i.e. both point to the same sectors on the hard drive,
and thus they are always identical, even if you change one).

http://codereview.appspot.com/5183042/diff/1/python/lilylib.py
File python/lilylib.py (right):

http://codereview.appspot.com/5183042/diff/1/python/lilylib.py#newcode154
python/lilylib.py:154: return x
Ah, so in windows you can give a command line argument argument of the
form
  my-cmd  \$"`
and the command will actually receive a string containing
backslash-dollar-doublequote-backtick?
And none of these characters (dollar, double quotes, backtick,
backslash) need to be escaped with a backslash? i.e. you don't need
  my-cmd "\\\$\"\`"
?

http://codereview.appspot.com/5183042/