Merge lp:~tycho-s/simplestreams/fix-1237990 into lp:~smoser/simplestreams/trunk

[Tycho Andersen]

=== modified file 'simplestreams/objectstores/__init__.py'
--- simplestreams/objectstores/__init__.py	2013-09-11 21:22:41 +0000
+++ simplestreams/objectstores/__init__.py	2013-10-10 15:00:45 +0000
@@ -106,7 +106,13 @@
                 # continuing not supported, just delete and retry
                 os.unlink(partfile)
 
-        with open(partfile, "ab") as wfp:
+        with open(partfile, "r+b") as wfp:
+            # read the first part of the file in to get the right checksum
+            while True:
+                buf = wfp.read(self.read_size)
+                cksum.update(buf)
+                if len(buf) < self.read_size:
+                    break
 
             while True:
                 buf = reader.read(self.read_size)