Support extra classpath with no inner jar specification

Currently one can only reference an inner jar with extra-classpath but
not the bundle itself.

As this is actually something useful and this is even used in platform
builds (even though it seem not effective due to this bug), PDE should
support it as well.

ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/RequiredPluginsClasspathContainer.java

@@ -522,18 +522,26 @@ protected void addExtraClasspathEntries(List<IClasspathEntry> entries, String[]
 				addExtraLibrary(path, null, entries);
 			} else {
 				int count = path.getDevice() == null ? 4 : 3;
-				if (path.segmentCount() >= count) {
+				int segments = path.segmentCount();
+				if (segments >= count - 1) {
 					String pluginID = path.segment(count - 2);
 					IPluginModelBase model = PluginRegistry.findModel(pluginID);
 					if (model != null && model.isEnabled()) {
 						path = path.setDevice(null);
 						path = path.removeFirstSegments(count - 1);
 						IResource underlyingResource = model.getUnderlyingResource();
 						if (underlyingResource == null) {
-							IPath result = PDECore.getDefault().getModelManager().getExternalModelManager()
-									.getNestedLibrary(model, path.toString());
-							if (result != null) {
-								addExtraLibrary(result, model, entries);
+							if (path.segmentCount() == 0) {
+								String installLocation = model.getInstallLocation();
+								if (installLocation != null) {
+									addExtraLibrary(IPath.fromOSString(installLocation), model, entries);
+								}
+							} else {
+								IPath result = PDECore.getDefault().getModelManager().getExternalModelManager()
+										.getNestedLibrary(model, path.toString());
+								if (result != null) {
+									addExtraLibrary(result, model, entries);
+								}
 							}
 						} else {
 							IFile file = underlyingResource.getProject().getFile(path);