[arch-general] update to calibre-0.9.15-1

[Alexander Bashmakov]

> don't remember if my internet connection went dead during the first attempt
> to update, that happens frequently. but i don't see how that would mess up
> things -- unless everything is downloaded & checked, pacman doesn't do
> anything.
>

It is common issue when you run as root python program without
precompiled pyc/pyo, now pyc/pyo provided by package and conflict with
autogenerated.