Add emacs mode-lines to ST sources

To each .c and .h file, add:

 /* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */

'gnu' is the default anyways for Emacs, but indent-tabs-mode is not,
so this sets things up to correspond to the policy of no-tabs.

http://bugzilla.moblin.org/show_bug.cgi?id=6467

src/st/st-scroll-view.c

@@ -1,3 +1,4 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
 /*
  * st-scroll-view.h: Container with scroll-bars
  *