Fix string comparisons using ==

There are a number of places where string comparisons are incorrectly done using ==.

1. nuxeo/nuxeo-core/nuxeo-core-api/src/main/java/org/nuxeo/ecm/core/utils/BlobsExtractor.java:174
   that latest one is a call to equals() with different types
   => I guess the check on the field name won't be done. I'm unsure about the result of "*".equals(field.getName()) but I don't think field.getName().toString() will be called.
2. nuxeo/nuxeo-core/nuxeo-core-api/src/main/java/org/nuxeo/ecm/core/utils/BlobsExtractor.java:312
   => the wanted logic is never satisfied
3. nuxeo/nuxeo-jsf/nuxeo-platform-webapp-base/src/main/java/org/nuxeo/ecm/webapp/directory/VocabularyTreeNode.java:197
   => I guess it's simply never satisfied but works thanks to line 200
4. nuxeo/nuxeo-jsf/nuxeo-platform-webapp-base/src/main/java/org/nuxeo/ecm/webapp/directory/DirectoryTreeNode.java:305
   => I guess it's simply never satisfied but works thanks to line 308
5. nuxeo/nuxeo-services/nuxeo-platform-ws/src/main/java/org/nuxeo/ecm/platform/ws/NuxeoRemotingBean.java:278
   => systematic call to rs.getDocumentManager().getSourceDocument(doc.getRef());