Add 'import site' to pythonXY._pth file, so .pth files are read

examples/console/installer.cfg

@@ -6,7 +6,7 @@ entry_point=guessnumber:main
 console=true
 
 [Python]
-version=3.5.1
+version=3.6.3
 bitness=64
 format=bundled
 

nsist/__init__.py

@@ -209,7 +209,7 @@ class InstallerBuilder(object):
                      and f.endswith('._pth')]
         for pth in pth_files:
             with open(pjoin(python_dir, pth), 'a+b') as f:
-                f.write(b'\r\n..\\pkgs\r\n')
+                f.write(b'\r\n..\\pkgs\r\nimport site\r\n')
 
         self.install_dirs.append(('Python', '$INSTDIR'))