Check for PlotSquared before initializing the feature class

Some users are experiencing issues during startup with FAWE not finding PlotSquared resulting in errors.

worldedit-bukkit/src/main/java/com/boydti/fawe/bukkit/FaweBukkit.java

@@ -325,6 +325,7 @@ public class FaweBukkit implements IFawe, Listener {
     }
 
     private void setupPlotSquared() {
+        if(this.plugin.getServer().getPluginManager().getPlugin("PlotSquared") == null) return;
         WEManager.IMP.managers.add(new com.boydti.fawe.bukkit.regions.plotsquared.PlotSquaredFeature());
         log.debug("Plugin 'PlotSquared' found. Using it now.");
     }