ThornDoc uses '==' within 'test' to test for something being equal. However, for shell scripts this should be '='. This works in bash, since it also accepts '==', but it does not work for /bin/sh by default, which is what ThornDoc claims to be a script for. The effect is that 'make THORN-ThornDoc' prints a lot of warnings.
The attached patch fixes this by replacing '==' with '='.