Handle the default interpreter's runtime exception.

include/cling/Interpreter/RuntimeExceptions.h

@@ -16,6 +16,7 @@ namespace cling {
     ///\brief Base class for all interpreter exceptions.
     ///
     class InterpreterException {
+    public:
       virtual void what() throw();
     };
 

lib/UserInterface/UserInterface.cpp

@@ -91,6 +91,10 @@ namespace cling {
 
       }
       catch(runtime::NullDerefException& e) {
+        llvm::errs() << "Exception was thrown at runtime. Recovering...\n";
+        e.what();
+      }
+      catch(runtime::InterpreterException& e) {
         // The diagnostic goes here:
         e.what();
       }