Do auto translation string matching at database level

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/autotranslate.py

@@ -50,13 +50,16 @@ def auto_translate(user, translation, source, inconsistent, overwrite):
             translation=translation
         )
 
+    # Filter by strings
+    units = units.filter(
+        source__in=sources.values('source')
+    )
+
     translation.commit_pending(None)
 
     for unit in units.iterator():
-        update = sources.filter(source=unit.source)
-        if update.exists():
-            # Get first entry
-            update = update[0]
+        # Get first matching entry
+        update = sources.filter(source=unit.source)[0]
         # No save if translation is same
         if unit.fuzzy == update.fuzzy and unit.target == update.target:
             continue