Okay, I went ahead and replaced the default 'com.avast.MacAvast.MAD' file with the 0.0.82-beta version as instructed.
I ran a manual scan with "/" as the only scan location in the preferences list. My understanding is that setting should scan the entire volume "Macintosh HD" and nothing else.
When the scan started it counted p the files as usual, I could not get the exact count as the count display disappears as soon at it completed counting and begins scanning, however my best estimate of the file count was just a tad under 600,000 files.
The scan reached that count in reasonable time. Again I didn't time it, but it was under an hour for certain. However instead of stopping there it next proceeded to scan my Time Capsule volume. I say 'Time Capsule' is a generic sort of way because it is not in fact an actual Apple Time Capsule, rather my Time Machine backs up to my HP Media Smart Server's Time capsule emulator (I don't know what else to call it, so I'll call it an emulator) mounted as Volumes/Backup to HP MediaSmart Server.
I can actually watch it being backed up so yes I am certain of this. Because this volume is mounted over Wifi, as you can imagine it took several hours for this scan to complete.
Once that volume completed the scan next moved onto 'Volumes/Windows' where I have my Bootcamp Windows Vista installed, Since I also have Avast for Windows installed there, I don't really need to OS/X installation scanning the Windows partition, but again there seems to be no way to avoid it. I gets scanned whether I select it or not. Of course I can avoid the scanning of the Time Machine volume simply by unmounting it prior to running the scan, however there is no good way to dismount the Windows volume that I am aware of since it resides in the same hard drive as the Macintosh HD volume.
I the end the scan did complete successfully with a total file count of 832,465. As usual there were a number of 'error' messages, but no infections detected.