Added test for multiple imports in distutils script.

This exposes a bug.

src/zc/buildout/easy_install.txt

@@ -977,6 +977,7 @@ like for the console_scripts.
       ]
     <BLANKLINE>
     <BLANKLINE>
+    import os
     import sys; sys.stdout.write("distutils!\n")
 
 Note that there are several items that need to come first in such a script

src/zc/buildout/tests.py

@@ -2947,6 +2947,7 @@ def create_sample_eggs(test, executable=sys.executable):
             '# -*- coding: utf-8 -*-\n'
             '"""Module docstring."""\n'
             'from __future__ import print_statement\n'
+            'import os\n'
             'import sys; sys.stdout.write("distutils!\\n")\n'
             )
         write(