Install pylauncher when target is Py 2, not build environment

Closes gh-23

nsist/__init__.py

@@ -273,7 +273,7 @@ from {module} import {func}
             if e.errno != errno.EEXIST:
                 raise e
         self.fetch_python()
-        if PY2:
+        if self.py_version < '3.3':
             self.fetch_pylauncher()
         
         self.prepare_shortcuts()

nsist/nsiswriter.py

@@ -27,7 +27,7 @@ class NSISFileWriter(object):
                 ';UNINSTALL_DIRECTORIES': self.dirs_uninstall,
                 ';UNINSTALL_SHORTCUTS': self.shortcuts_uninstall,
         }
-        if PY2:
+        if installerbuilder.py_version < '3.3':
             self.template_fields.update({
                 ';PYLAUNCHER_INSTALL': self.pylauncher_install,
                 ';PYLAUNCHER_HELP': self.pylauncher_help})