Improve the Mail metadata extractor test with more checks, and add a general metadata 'did we get something back' check to fail earlier with a more helpful error message. Also added an Array -> Collection TypeConverter that was missing from an early branch port

git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@18698 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

source/java/org/alfresco/repo/content/metadata/AbstractMetadataExtracterTest.java

@@ -103,6 +103,8 @@ public abstract class AbstractMetadataExtracterTest extends TestCase
         try
         {
             Map<QName, Serializable> properties = extractFromMimetype(mimetype);
+            // check we got something
+            assertFalse("extractFromMimetype should return at least some properties, none found", properties.isEmpty());
             // check common metadata
             testCommonMetadata(mimetype, properties);
             // check file-type specific metadata