Ensure activate does not re-enter

plugins/brackets-completion/brackets-completion.vala

@@ -35,6 +35,7 @@ public class Scratch.Plugins.BracketsCompletion : Scratch.Plugins.PluginBase {
         base (info, iface);
     }
 
+    ulong doc_hook_handler = 0;
     protected override void activate_internal () {
         brackets = new Gee.HashMap<string, string> ();
         brackets["("] = ")";
@@ -59,7 +60,7 @@ public class Scratch.Plugins.BracketsCompletion : Scratch.Plugins.PluginBase {
     }
 
     protected override void deactivate_internal () {
-        iface.hook_document.disconnect (on_hook_document);
+        this.disconnect (doc_hook_handler);
     }
 
     void on_hook_document (Scratch.Services.Document doc) {

plugins/highlight-word-selection/highlight-word-selection.vala

@@ -35,7 +35,6 @@ public class Scratch.Plugins.HighlightSelectedWords : Scratch.Plugins.PluginBase
     ulong window_hook_handler = 0;
     ulong doc_hook_handler = 0;
     protected override void activate_internal () {
-        // plugins = (Scratch.Plugins.Interface) object;
         doc_hook_handler = iface.hook_document.connect ((doc) => {
             if (current_source != null) {
                 current_source.deselected.disconnect (on_deselection);

plugins/word-completion/plugin.vala

@@ -48,9 +48,6 @@ public class Scratch.Plugins.Completion : Scratch.Plugins.PluginBase {
     ulong window_hook_handler = 0;
     ulong doc_hook_handler = 0;
     protected override void activate_internal () {
-        if (window_hook_handler > 0) {
-            return;
-        }
         parser = new Euclide.Completion.Parser ();
         window_hook_handler = iface.hook_window.connect ((w) => {
             this.main_window = w;

src/Services/PluginManager.vala

@@ -32,12 +32,20 @@ public abstract class Scratch.Plugins.PluginBase : GLib.Object {
     }
 
     public void activate () {
+        if (is_active) {
+            return;
+        }
+
         is_active = true;
         activate_internal ();
     }
 
 
     public void deactivate () {
+        if (!is_active) {
+            return;
+        }
+
         is_active = false;
         deactivate_internal ();
     }