Add warning for dead_actute warning.

Yo dawg, I herd you like warnings!

qutebrowser/app.py

@@ -65,7 +65,8 @@ from qutebrowser.config.iniparsers import ReadWriteConfigParser
 from qutebrowser.config.lineparser import LineConfigParser
 from qutebrowser.browser.cookies import CookieJar
 from qutebrowser.utils.message import MessageBridge
-from qutebrowser.utils.misc import dotted_getattr, get_standard_dir
+from qutebrowser.utils.misc import (dotted_getattr, get_standard_dir,
+                                    actute_warning)
 from qutebrowser.utils.debug import set_trace  # pylint: disable=unused-import
 
 
@@ -122,6 +123,7 @@ class QuteBrowser(QApplication):
         self._args = self._parse_args()
         self._init_log()
         self._init_misc()
+        actute_warning()
         self._init_config()
         self._init_modes()
         websettings.init()

qutebrowser/utils/misc.py

@@ -155,3 +155,18 @@ def get_standard_dir(typ):
     if not os.path.exists(path):
         os.makedirs(path)
     return path
+
+
+def actute_warning():
+    """Display a warning about the dead_actute issue if needed."""
+    if not (sys.platform.startswith('linux') and
+            os.path.exists('/usr/share/X11/locale/en_US.UTF-8/Compose')):
+        return
+    with open('/usr/share/X11/locale/en_US.UTF-8/Compose', 'r') as f:
+        for line in f:
+            if '<dead_actute>' in line:
+                print("Note: If you got a 'dead_actute' warning above, that "
+                      "is not a bug in qutebrowser! See "
+                      "https://bugs.freedesktop.org/show_bug.cgi?id=69476 for "
+                      "details.")
+                break