Syntax: Tone down warning about tabs to a status message

In unknown situations, the check can be triggered more frequently and
become quite annoying. Additionally, it's not like we *must* play the
police here and enforce usage of the correct indentation settings when
tooling around syntax tests will break by itself already.

Closes #390

plugins/syntaxtest_dev.py

@@ -83,9 +83,9 @@ def __del__(self):
         # or plugin was unloaded.
         # Complain about the former, if we have a test file.
         if self.header and not self.is_applicable(self.view.settings()):
-            sublime.error_message((
+            sublime.status_message((
                 "Syntax tests do not work properly with tabs as indentation."
-                "\n\nYou MUST use spaces!"
+                " You MUST use spaces!"
             ))
 
     def on_modified_async(self):