Bug: 459051 [xtext][linking] Maintain information about compile time constants

Added a hook to execute logic after the final linking was done
in the batch type resolution (addDeferredLogic()).
Not exposed as (provisional) API yet.

Also: 
- Don’t forget the root cause if something goes wrong during
  resource storage write operation
- Yet another NPE guard for default packages and type lookup

Change-Id: I26bff265485584f56f615fb3a7c7c60562992ec6

plugins/org.eclipse.xtext/src/org/eclipse/xtext/resource/persistence/ResourceStorageWritable.xtend

@@ -41,7 +41,11 @@ import org.eclipse.xtext.nodemodel.serialization.SerializationConversionContext
 		} catch (IOException e) {
 			LOG.error(e.message, e)
 		} finally {
-			zipOut.close
+			try {
+				zipOut.close
+			} catch(IOException e) {
+				LOG.error(e.message, e)	
+			}
 		}
 	}