* forward.test: Constrain the max recursion depth around recursive forwards, so that we do not run into early crashes on systems with limited stack sizes (when the stack is saturated before a recursion limit is hit). This fixes test runs on MinGW/ gcc builds at AppVeyor.
* forward.tests: Provide some background comment on platform-dependent error messages as test conditions (infinite loop) and make sure tests under 8.6 are executed as intended.