Fix error if script contains null byte. (backport from trunk)

--HG--
branch : setuptools-0.6
extra : convert_revision : svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/sandbox/branches/setuptools-0.6%4053814

setuptools/command/easy_install.py

@@ -1460,7 +1460,7 @@ def is_python(text, filename='<string>'):
     "Is this string a valid Python script?"
     try:
         compile(text, filename, 'exec')
-    except SyntaxError:
+    except (SyntaxError, TypeError):
         return False
     else:
         return True