Add test case for the bug which was in mgu of TFun

Here's another test case for the instance of the bug you fixed in mgu of EApp. (the fix was in two locations and your added test only exposes the bug in one of them)
Btw before noticing your fix fork we also stumbled on the same bug.. Next time I should look on the forks networks..
Cheers! Yair / Lamdu