Bug 804536 - Fix virtualenv population on Windows; r=glandium

I'm pretty sure the previous code works on Python 2.7.3. This
patch may break Python 3 compatibility. We'll cross that
bridge when we come to it.

build/virtualenv/populate_virtualenv.py

@@ -137,7 +137,7 @@ class VirtualenvManager(object):
         into the wrong place. This is how virtualenv's work.
         """
         packages = []
-        fh = open(self.manifest_path, 'rUt')
+        fh = open(self.manifest_path, 'rU')
         for line in fh:
             packages.append(line.rstrip().split(':'))
         fh.close()