stack trace when a file cannot be locked

[bfrk]

This mostly concerns use of vdct in batch mode to flatten hierarchical vdb files. It seems when using parallel make (-j option) the already running instance takes a file lock leading to ugly stack traces like the one below. These are not helpful for users, instead a simple one line message would be better.

java.util.prefs.BackingStoreException: Couldn't get file lock.
at java.util.prefs.FileSystemPreferences.sync(FileSystemPreferences.java:715)
at com.cosylab.vdct.Settings.sync(Unknown Source)
at com.cosylab.vdct.Settings.setSnapToGrid(Unknown Source)
at com.cosylab.vdct.graphics.objects.Group.initializeLayout(Unknown Source)
at com.cosylab.vdct.graphics.DrawingSurface.applyVisualData(Unknown Source)
at com.cosylab.vdct.vdb.VDBData.generateTemplate(Unknown Source)
at com.cosylab.vdct.vdb.VDBData.extractTemplates(Unknown Source)
at com.cosylab.vdct.vdb.VDBData.generateVDBDataInternal(Unknown Source)
at com.cosylab.vdct.vdb.VDBData.generateTemplate(Unknown Source)
at com.cosylab.vdct.vdb.VDBData.extractTemplates(Unknown Source)
at com.cosylab.vdct.vdb.VDBData.generateVDBDataInternal(Unknown Source)
at com.cosylab.vdct.vdb.VDBData.generateTemplate(Unknown Source)
at com.cosylab.vdct.vdb.VDBData.generateVDBData(Unknown Source)
at com.cosylab.vdct.graphics.DrawingSurface.open(Unknown Source)
at com.cosylab.vdct.graphics.DrawingSurface.open(Unknown Source)
at com.cosylab.vdct.graphics.DrawingSurface.open(Unknown Source)
at com.cosylab.vdct.GenerateFlatDatabase.flatDatabase(Unknown Source)
at com.cosylab.vdct.GenerateFlatDatabase.main(Unknown Source)

A related issue is that in flattening mode vdct outputs a lot of mostly irrelevant stuff even if no error happens. A command line switch (-q) or an optional argument for the method call would be very much appreciated.