Core: multiple instances of OpenDataset warning

[jsnel]

Although it doesn't affect the functionality of Glotaran it does pollute the log file in case people want to report real bugs. Would be great if it could be fixed.

java.lang.IllegalStateException: Warning: multiple instances of shared class org.glotaran.core.main.nodes.actions.OpenDataset created.
[catch] at org.openide.util.SharedClassObject.(SharedClassObject.java:202)
at org.openide.util.actions.SystemAction.(SystemAction.java:87)
at org.openide.util.actions.CallableSystemAction.(CallableSystemAction.java:70)
at org.openide.util.actions.NodeAction.(NodeAction.java:96)
at org.openide.util.actions.CookieAction.(CookieAction.java:77)
at org.glotaran.core.main.nodes.actions.OpenDataset.(OpenDataset.java:40)
at org.glotaran.core.main.nodes.TGDatasetNode.getActions(TGDatasetNode.java:75)
at org.openide.nodes.FilterNode.getActions(FilterNode.java:751)
at org.openide.nodes.NodeOp.findActions(NodeOp.java:162)
at org.openide.explorer.view.TreeView.createPopup(TreeView.java:1056)
at org.openide.explorer.view.TreeView$PopupAdapter.showPopup(TreeView.java:1555)
at org.openide.awt.MouseUtils$PopupMouseAdapter.maybePopup(MouseUtils.java:189)
at org.openide.awt.MouseUtils$PopupMouseAdapter.mousePressed(MouseUtils.java:180)
at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:280)
at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:279)
at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:279)
at java.awt.Component.processMouseEvent(Component.java:6522)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6290)
at java.awt.Container.processEvent(Container.java:2234)
at java.awt.Component.dispatchEventImpl(Component.java:4881)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4530)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
at java.awt.Container.dispatchEventImpl(Container.java:2278)
at java.awt.Window.dispatchEventImpl(Window.java:2739)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
at java.awt.EventQueue.access$400(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:697)
at java.awt.EventQueue$3.run(EventQueue.java:691)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:719)
at java.awt.EventQueue$4.run(EventQueue.java:717)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:159)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

[jsnel]

This might be helpful:
WARNING [org.openide.util.SharedClassObject]: (Run with -J-Dorg.openide.util.SharedClassObject.level=0 for more details.)