If "tac" doesn't exist (e.g., on non GNU/Linux systems like OS X & other...

If "tac" doesn't exist (e.g., on non GNU/Linux systems like OS X & other BSDs), emulate with sed '1!G;h;$!d' (from http://www.catonmat.net/blog/sed-one-liners-explained-part-one/)

Since the Makefile executes tests using "sh" instead of "bash", use the more portable "> obs 2>&1" instead of "&> obs" so the test will pass when /bin/sh isn't bash (e.g., on Debian-based Linux distributions, and most non-Linux *nix systems).