Removes the ComException wrapping of server-side BranchedDataException

which is no longer needed due to recent changes in exception streaming
from server to client. In fact the wrapping prevented a slave to properly
react to branched data and would make that slave unable to ever join the
cluster.
Merge pull request #1870 from tinwelint/1.9-branched-slave-fix

Removes the ComException wrapping of server-side BranchedDataException