return the just-added tool from addTool

augment addTool to return the tool it just added.
This allows one to write:
```python
myToolWithName = myalg.addTool(tool_conf2,"ToolWithName")
myToolWithName.String = "xyz"
```
instead of 
```python
myalg.addTool(tool_conf2,"ToolWithName")
myalg.ToolWithName.String = "xyz"
```
which requires one to duplicate the "ToolWithName" -- once as string, and
once as attribute, but only rarely does anybody use getattr for the 2nd
case to just avoid the duplication.

Of course, one could write 
```python
myalg.addTool(tool_conf2,"ToolWithName", String="xyz")
```
or even pass in a complete dictionary with **, but the configuration of
the tool isn't necessarily complete at the time of creation of its
configurable.

Fixes GAUDI-1162.
See merge request !87

GaudiExamples/options/AlgTools.py

@@ -36,9 +36,14 @@ tool_conf2 = MyTool( 'MyTool_conf2',
                      OutputLevel = INFO )
 
 
-myalg.addTool(tool_conf2,"ToolWithName")
+myToolWithName = myalg.addTool(tool_conf2,"ToolWithName")
 
-myalg.ToolWithName.String = "abc"
+myalg.ToolWithName.String = "xyz"
+
+assert myToolWithName.String == "xyz"
+assert myalg.ToolWithName == myToolWithName
+
+myToolWithName.String = "abc"
 
 mygalg = MyGaudiAlgorithm('MyGaudiAlg')
 mygalg.PrivToolHandle.String = "Is a private tool"

GaudiKernel/python/GaudiKernel/Configurable.py

@@ -786,6 +786,7 @@ class Configurable( object ):
         if name in self.__slots__:
             # this is to avoid that the property hides the tool
             setattr(self,name,self.__tools[name])
+        return self.__tools[name]
 
     def _isInSetDefaults( self ):
         return self._inSetDefaults