MigrationService: Clearer error msg for faulty providers

Issue-Ref: 3541
Issue-Url: https://af3-developer.fortiss.org/issues/3541


Signed-off-by: Alexander Diewald <diewald@fortiss.org>

org.fortiss.tooling.kernel/src/org/fortiss/tooling/kernel/internal/.ratings

@@ -7,7 +7,7 @@ ElementCompositorService.java 98c5d27e09881e60aa4f87c1ac0c7787cdec9f7c GREEN
 LibraryPrototypeProvider.java b77eddbdca78f561ffb1233e98817be361c690ae GREEN
 LibraryService.java d22671ba820466062852c15873698adf28960d94 GREEN
 LoggingService.java da784259f7b456b54bf75c41ec268f64919ce78d GREEN
-MigrationService.java 2f800eac9793aa736089a802bbfc2c4c1c09770d GREEN
+MigrationService.java 8df3452b6dd58424ee581fc7ac4f801244e8d63b YELLOW
 PersistencyService.java 2e3936012a9b7217a293cbe8272ffa5f02518045 GREEN
 PrototypeService.java cf8e6fa96ba9c2f65b24400054ed68e93238a975 GREEN
 ToolingKernelInternal.java f6e7114825748683c7f1d040b41ab854a6c4d79b GREEN

org.fortiss.tooling.kernel/src/org/fortiss/tooling/kernel/internal/MigrationService.java

@@ -118,7 +118,8 @@ public class MigrationService extends ObjectAwareServiceBase<IMigrationProvider>
 						error(ToolingKernelActivator.getDefault(),
 								"Migrating " + input.getSaveableName() + " failed: A need for " +
 										"migration is indicated although the migration was " +
-										"already performed. Please fix the migrator (or model).");
+										"already performed. Please fix the migrator " +
+										provider.getClass().getSimpleName() + " or the model.");
 					}
 				}
 				unknownFeatures.entrySet().removeAll(migratedFeatures.entrySet());