The unittests now compile exception_Backtrace.o and now work again.

test/unittest/Makefile

@@ -93,6 +93,7 @@ rununittests: $(RMC_OBJECTS) \
   dlf_Param.o \
   dlf_dlf_lib.o \
   exception_AlreadyInitialized.o \
+  exception_Backtrace.o \
   exception_Communication.o \
   exception_DismountFailed.o \
   exception_Exception.o \
@@ -522,6 +523,10 @@ exception_AlreadyInitialized.o: \
   $(ROOT_DIR)/castor/exception/AlreadyInitialized.cpp
 	g++ $(COMMON_OPS) -c $(INCLUDE_OPS) -o $@ $^
 
+exception_Backtrace.o: \
+  $(ROOT_DIR)/castor/exception/Backtrace.cpp
+	g++ $(COMMON_OPS) -c $(INCLUDE_OPS) -o $@ $^
+
 exception_Communication.o: $(ROOT_DIR)/castor/exception/Communication.cpp
 	g++ $(COMMON_OPS) -c $(INCLUDE_OPS) -o $@ $^