EclipsePreferences: intern() keys and values

removes all duplicate Strings from
JavaModelManager.PerProjectInfo.options

eclipse-jdt/eclipse.jdt.core#1692

bundles/org.eclipse.equinox.preferences/src/org/eclipse/core/internal/preferences/EclipsePreferences.java

@@ -625,6 +625,11 @@ protected IEclipsePreferences internalNode(String path, boolean notify, Object c
 	 * null if no value existed.
 	 */
 	protected String internalPut(String key, String newValue) {
+		// intern the Strings to save memory
+		// shareStrings() comes too late,
+		// when plugins may have already copied preferences
+		newValue = newValue.intern();
+		key = key.intern();
 		synchronized (childAndPropertyLock) {
 			// illegal state if this node has been removed
 			checkRemoved();