linux: Only use Gtk.ShowUri in flatpaks

SparkleShare/Linux/About.cs

@@ -103,7 +103,7 @@ namespace SparkleShare {
                 Xalign = 0, Xpad = 0
             };
 
-            if (InstallationInfo.Directory.StartsWith ("/app", StringComparison.InvariantCulture))
+            if (InstallationInfo.IsFlatpak)
                 version.Text += " (Flatpak)";
 
             updates = new Label ("Checking for updates…") {

SparkleShare/Linux/Controller.cs

@@ -98,7 +98,10 @@ namespace SparkleShare {
 
         public override void OpenFile (string path)
         {
-            Global.ShowUri (Gdk.Screen.Default, path);
+            if (InstallationInfo.IsFlatpak)
+                Global.ShowUri (Gdk.Screen.Default, path);
+            else
+                new Command ("xdg-open", string.Format ("\"{0}\"", path)).Start ();
         }
 
 

SparkleShare/Linux/UserInterface.cs

@@ -120,3 +120,4 @@ namespace SparkleShare
         }
     }
 }
+

Sparkles/InstallationInfo.cs

@@ -95,5 +95,12 @@ namespace Sparkles {
                 return version.Substring (0, version.Length - 2);
             }
         }
+
+
+        public static bool IsFlatpak {
+            get {
+                return Directory.StartsWith ("/app", StringComparison.InvariantCulture);
+            }
+        }
     }
 }