[Therion] Background zoom-level bug

[Olly Betts]

On Mon, Nov 12, 2018 at 09:22:59PM +1300, Bruce Mutton via Therion wrote:
> This bug has been around ever since mouse wheel zooming was
> introduced.  An attempt was made to fix it I recall, but it did not
> have the desired effect.
> It manifests for bitmap background images, but not for xvi 'images'.
> A work around is to never roll the mouse wheel when working with th2
> with bitmaps inserted.  Very hard to do!.

There have been (at least) two changes that apparently fix bugs with
zooming in xtherion using the mouse wheel since the last release:

https://github.com/therion/therion/commit/82fc78e8931d36b215ab676754ede0cc54d3935d
https://github.com/therion/therion/commit/99d3347abaa96dde6ef3ba702a6040da65612e8c

It's been more than 18 months since the last release, and there are
a significant number of changes (~150 commits ignoring merge commits)
- perhaps it's time to make a new release?

It would be useful to have one before the end of the year from a Debian 
perspective so we can get it into the next stable release.

Cheers,
    Olly