Deduplicate launch configs

The same launch config might be returned by multiple
LaunchShortcutExtension and is then shown twice.

This simply filter items that where already seen to deduplicate such
entries.

Fix eclipse-platform#527

debug/org.eclipse.debug.ui/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: %pluginName
 Bundle-SymbolicName: org.eclipse.debug.ui; singleton:=true
-Bundle-Version: 3.18.300.qualifier
+Bundle-Version: 3.18.400.qualifier
 Bundle-Activator: org.eclipse.debug.internal.ui.DebugUIPlugin
 Bundle-Vendor: %providerName
 Bundle-Localization: plugin

debug/org.eclipse.debug.ui/ui/org/eclipse/debug/ui/actions/ContextualLaunchAction.java

@@ -15,11 +15,13 @@
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Set;
 
 import org.eclipse.core.expressions.Expression;
 import org.eclipse.core.expressions.IEvaluationContext;
@@ -280,9 +282,12 @@ protected void fillMenu(Menu menu) {
 			}
 		}
 		// now add collected launches
+		Set<ILaunchConfiguration> added = new HashSet<>();
 		for (Entry<LaunchShortcutExtension, ILaunchConfiguration[]> entry : launchConfigurations.entrySet()) {
 			for (ILaunchConfiguration configuration : entry.getValue()) {
-				populateMenuItem(fMode, entry.getKey(), menu, configuration, accelerator++, null);
+				if (added.add(configuration)) {
+					populateMenuItem(fMode, entry.getKey(), menu, configuration, accelerator++, null);
+				}
 			}
 		}