Update maintenance scripts to abort if the check-release target fails to complete.

Maintenance/makefile

@@ -11,7 +11,7 @@
 LUFA_ROOT = ../
 
 upgrade-doxygen:
-	@echo Updating Doxygen.conf files...
+	@echo Upgrading Doxygen.conf files...
 	@for doxygen_conf in `find $(LUFA_ROOT) -name Doxygen.conf`; do \
 	  doxygen -u $$doxygen_conf; \
 	done;
@@ -21,8 +21,10 @@ check-release:
 	@echo Checking for release suitability...
 	@if ( grep "XXXXXX" $(LUFA_ROOT)/LUFA/DoxygenPages/*.txt > /dev/null ;); then \
 	  echo "  ERROR: Doxygen documentation has not been updated for release!"; \
+	  exit 1; \
 	fi;
 	@if ( grep "000000" $(LUFA_ROOT)/LUFA/Version.h > /dev/null ;); then \
 	  echo "  ERROR: Version header has not been updated for release!"; \
+	  exit 1; \
 	fi;
 	@echo Done.