Change 'identifier' target to use printf not echo

Prior to this change, the non-portable `echo -n` was used to list the
offending files without a project identifier during `make identifier`.
The proper way to do this is use printf.

This resolves issue #1.

Makefile

@@ -97,7 +97,7 @@ static:
 #                   also removes old submit tarballs, they are outdated
 identifier:
 	@if [ $$(grep --include=*.{h,hpp,c,cpp} --exclude=xcode_redirect.hpp --directories=skip -L $(IDENTIFIER) * | wc -l) -ne 0 ]; then \
-		echo "Missing project identifier in file(s): \c"; \
+		printf "Missing project identifier in file(s): "; \
 		echo `grep --include=*.{h,hpp,c,cpp} --directories=skip -L $(IDENTIFIER) *`; \
 		rm -f $(PARTIAL_SUBMITFILE) $(FULL_SUBMITFILE); \
 		exit 1; \