Change most uses of os.system to use subprocess

The only places left that use os.system are in ImageShow and setup.py

PIL/GifImagePlugin.py

@@ -333,13 +333,20 @@ def _save_netpbm(im, fp, filename):
     # below for information on how to enable this.
 
     import os
+    from subprocess import Popen, check_call, PIPE
     file = im._dump()
     if im.mode != "RGB":
-        os.system("ppmtogif %s >%s" % (file, filename))
+        with open(filename, 'wb') as f:
+            check_call(["ppmtogif", file], stdout=f)
     else:
-        os.system("ppmquant 256 %s | ppmtogif >%s" % (file, filename))
-    try: os.unlink(file)
-    except: pass
+        with open(filename, 'wb') as f:
+            #TODO: What happens if ppmquant fails?
+            ppmquant_proc = Popen(["ppmquant", "256", file], stdout=PIPE)
+            check_call(["ppmtogif"], stdin=ppmquant_proc.stdout, stdout=f)
+    try:
+        os.unlink(file)
+    except:
+        pass
 
 
 # --------------------------------------------------------------------

PIL/JpegImagePlugin.py

@@ -360,12 +360,14 @@ class JpegImageFile(ImageFile.ImageFile):
 
         # ALTERNATIVE: handle JPEGs via the IJG command line utilities
 
+        import subprocess
         import tempfile
         import os
         f, path = tempfile.mkstemp()
         os.close(f)
         if os.path.exists(self.filename):
-            os.system("djpeg %s > '%s'" % (quote(self.filename), path))
+            with open(path, 'wb') as f:
+                subprocess.check_call(["djpeg", self.filename], stdout=f)
         else:
             raise ValueError("Invalid Filename")
 
@@ -608,8 +610,10 @@ def _save(im, fp, filename):
 def _save_cjpeg(im, fp, filename):
     # ALTERNATIVE: handle JPEGs via the IJG command line utilities.
     import os
-    file = im._dump()
-    os.system("cjpeg %s >%s" % (file, filename))
+    import subprocess
+    tempfile = im._dump()
+    with open(filename, 'wb') as f:
+        subprocess.check_call(["cjpeg", tempfile], stdout=f)
     try:
         os.unlink(file)
     except: