Work around composer info label being too long. Fixes Bug 790435.

* ui/composer-widget.ui: Make the info label esliipsisable, but give it a
  reasonable minimum size.

* src/client/composer/composer-widget.vala (ComposerWidget): Set the info
  label's tooltip with the text so it can still be read when ellipsed.

src/client/composer/composer-widget.vala

@@ -2046,6 +2046,7 @@ public class ComposerWidget : Gtk.EventBox {
         }
 
         this.info_label.set_text(text);
+        this.info_label.set_tooltip_text(text);
     }
 
     // Updates from combobox contents and visibility, returns true if

ui/composer-widget.ui

@@ -762,6 +762,8 @@
               <object class="GtkLabel" id="info_label">
                 <property name="visible">True</property>
                 <property name="can_focus">True</property>
+                <property name="ellipsize">end</property>
+                <property name="width_chars">6</property>
                 <style>
                   <class name="dim-label"/>
                 </style>