transaction: do not overwrite atomic-temp files on error

Even though the original files can be restored from the backup, it should be
better to not write back a temporary file if we know it can be corrupted.

mercurial/transaction.py

@@ -347,9 +347,13 b' class transaction(util.transactional):'
                     files.append(vfs(name, 'w', atomictemp=True,
                                      checkambig=checkambig))
                 genfunc(*files)
+                for f in files:
+                    f.close()
+                # skip discard() loop since we're sure no open file remains
+                del files[:]
             finally:
                 for f in files:
-                    f.close()
+                    f.discard()
         return any
 
     @active