Make /storage/filesystem ignore .tmp files

Hardcode to ignore files with `.tmp` suffix as this is mentioned
in the vdir specification.

Author: bernhardreiter

vdirsyncer/storage/filesystem.py

@@ -80,7 +80,8 @@ def _get_href(self, ident):
     def list(self):
         for fname in os.listdir(self.path):
             fpath = os.path.join(self.path, fname)
-            if os.path.isfile(fpath) and fname.endswith(self.fileext):
+            if os.path.isfile(fpath) and fname.endswith(self.fileext) and (
+                    not fname.endswith('.tmp')):
                 yield fname, get_etag_from_file(fpath)
 
     def get(self, href):