Rev 5391 adds the anti-alias filtered speaker toggle emulation that was submitted to MAMEdev in May and ignored because it was MESS-only-in-common-code and nobody spoke up for it smile

It's a noticable difference and I also hooked it up to the Apple II series where it sounds much better and fixes a long-time issue with the mixing on the IIgs (the DC offset from the raw unfiltered speaker toggle was reducing the available headroom for the ES5503).