Donor defined on gauged model node turns the node into ungauged at Calibration

The feature #92 (closed) which introduced the user defined "donor" column in GRiwrm for defining manually donor nodes for ungauged nodes does not forbid to define donor for gauged nodes. Moreveor, documentation related to feature #156 (closed) which allows to define a priori nodes other than upstream nodes propose to use this same column for forcing node sequence order at calibration when the sibling a priori node is not processed before the current node.

2 bugs are identified:

• Gauged nodes with user defined donor are turned into ungauged node at calibration
• The number of parameter depending on upstream/intermadiate node is not handled