No, this isn't a quickie, direct-to-video sequel, cashing in on the success of the 1977 animated hit about adventurous mice, but a full-blown theatrical effort. This time around, Bernard (voiced by Bob Newhart) is trying to pop the question to Bianca (Eva Gabor) when they're summoned to Australia, where a young boy has been kidnapped by a pallid, gray-faced poacher (who looks like and is …