No error when rom file is missing

[Roland09]

When a rom isn't found an error should be displayed. It would also be nice to see the folder in which the rom is being searched.

[xantari]

I'm not sure if it's possible, but it would also be nice if it would also tell you if it was found but the hash signature doesn't match.

For instance, there were a lot of forum postings for Dr Who, because the ROM was re-dumped and the one that worked in PinMAME 3.2 didn't work in 3.3 (no sound was being output). You had to go find the new dump of that ROM.