Removes popen3 deprecated warning (issue 6471043)

[PhilEHolmes]

Reviewers: Graham Percival, John Mandereau,

Message:
Please review

Description:
I tested this on windows by adding a call to Popen (just opening
notepad) at the start of lilypond-book.  This is why we need the
conditional test for fds-close - windows does not allow this to be True
when used with the stdin, etc., options.  This is running the python
instance that is delivered with the current lilypond.  I have also run
make, make doc and confirmed that the deprecation warning is taken out.

Please review this at http://codereview.appspot.com/6471043/

Affected files:
  M python/book_snippets.py


Index: python/book_snippets.py
diff --git a/python/book_snippets.py b/python/book_snippets.py
index  
f3a11ccca94fa97d5967fb286de53290ab1e604f..69fdc4fa6867401cdcd40fecbf16b4e6324ed4b7  
100644
--- a/python/book_snippets.py
+++ b/python/book_snippets.py
@@ -7,11 +7,8 @@ import re
 import os
 import copy
 import shutil
-# TODO: We are using os.popen3, which has been deprecated since python  
2.6. The
-# suggested replacement is the Popen function of the subprocess module.
-# Unfortunately, on windows this needs the msvcrt module, which doesn't  
seem
-# to be available in GUB?!?!?!
-# from subprocess import Popen, PIPE
+import subprocess
+import sys

 progress = ly.progress
 warning = ly.warning
@@ -740,10 +737,11 @@ printing diff against existing file." % filename)

         debug (_ ("Running through filter `%s'") % cmd, True)

-        # TODO: Use Popen once we resolve the problem with msvcrt in  
Windows:
-        (stdin, stdout, stderr) = os.popen3 (cmd)
-        # p = Popen(cmd, shell=True, stdin=PIPE, stdout=PIPE, stderr=PIPE,  
close_fds=True)
-        # (stdin, stdout, stderr) = (p.stdin, p.stdout, p.stderr)
+        closefds = True
+        if (sys.platform == "mingw32"):
+            closefds = False
+        p = subprocess.Popen(cmd, shell=True, stdin=subprocess.PIPE,  
stdout=subprocess.PIPE, stderr=subprocess.PIPE, close_fds=closefds)
+        (stdin, stdout, stderr) = (p.stdin, p.stdout, p.stderr)
         stdin.write (input)
         status = stdin.close ()