Thumbnails: support thumbnailing PNGs in palette mode
Right now this causes a rather mysterious error message: `IOError: cannot write mode P as JPEG`

diff --git a/plugins/thumbnails/server/worker.py b/plugins/thumbnails/server/worker.py
index 3bf935208..2ddb71850 100644
--- a/plugins/thumbnails/server/worker.py
+++ b/plugins/thumbnails/server/worker.py
@@ -108,7 +108,7 @@ def createThumbnail(width, height, crop, fileId, attachToType, attachToId):
     uploadModel = ModelImporter.model('upload')
 
     out = six.BytesIO()
-    image.save(out, 'JPEG', quality=85)
+    image.convert('RGB').save(out, 'JPEG', quality=85)
     size = out.tell()
     out.seek(0)
 
['plugins/thumbnails/server/worker.py']