bug#63949: 30.0.50; `vc-print-log´ does not erase buffer when called from *vc-change-log* buffer, at least for CVS logs

[Jens Schmidt]

> This code is very old, so at the very least we need to track its 
> origin and understand why it was added, before discussing whether it 
> should be removed. [...]

Totally agreed.  Pls ignore my patches for the time being, I just hacked
them together before really thinking and getting to the root cause of my
issues.  I'm trying to get into contact with Nathan, the author of the
enhancement that caused the regression, to see whether he can provide
more information than what is contained in his bug#40967.