41: Name clash if CheckRule Variable is named 'e' 

Also for CheckRule the name of the variable for the exception is
generated on the base of the rule's name.

Closes #41

Change-Id: Icd2ac5612ed735011735a464ea7679f4de26b947
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/41
regenerated example code

Change-Id: I6beac0d08a5104cee3dfc0921ec3c9ab5ca75965
Task-Url: https://github.com/LorenzoBettini/xsemantics/issues/issue/41