tests: Don't require bash.

Instead merge continuous regions of colored output. This way different
shell implementations shouldn't make a difference.

tests/example_simple.sh

@@ -1,7 +1,4 @@
-#!/bin/bash
-
-# Use bash to get consistent test results, /bin/sh can point to multiple
-# shells with different behaviour.
+#!/bin/sh
 
 # Copyright (C) 2013  Simon Ruderich
 #