Use the correct metadata backup implementation

src/calibre/db/__init__.py

@@ -136,8 +136,7 @@ def get_db_loader():
                     columns/categories/searches info into
                     self.field_metadata.
     2. Port library/restore.py
-    3. Replace the metadatabackup thread with the new implementation when using the new backend.
-    4. Check that content server reloading on metadata,db change, metadata
+    3. Check that content server reloading on metadata,db change, metadata
     backup, refresh gui on calibredb add and moving libraries all work (check
     them on windows as well for file locking issues)
 '''

src/calibre/gui2/library/models.py

@@ -21,7 +21,7 @@
 from calibre.utils.icu import sort_key
 from calibre.utils.search_query_parser import SearchQueryParser
 from calibre.db.search import _match, CONTAINS_MATCH, EQUALS_MATCH, REGEXP_MATCH
-from calibre.library.caches import (MetadataBackup, force_to_bool)
+from calibre.library.caches import force_to_bool
 from calibre.library.save_to_disk import find_plugboard
 from calibre import strftime, isbytestring
 from calibre.constants import filesystem_encoding, DEBUG, config_dir
@@ -234,6 +234,10 @@ def col_idx(name):
         self.start_metadata_backup()
 
     def start_metadata_backup(self):
+        if hasattr(self.db, 'new_api'):
+            from calibre.db.backup import MetadataBackup
+        else:
+            from calibre.library.caches import MetadataBackup
         self.metadata_backup = MetadataBackup(self.db)
         self.metadata_backup.start()
 
@@ -1209,7 +1213,6 @@ def __init__(self, parent):
         self.book_in_library = None
         self.sync_icon = QIcon(I('sync.png'))
 
-
     def counts(self):
         return Counts(len(self.db), len(self.db), len(self.map))
 
@@ -1613,3 +1616,4 @@ def set_editable(self, editable):
 # }}}
 
 
+