[pacman-dev] installing two packages conflicting with each other

[Xavier]

http://bugs.archlinux.org/task/7415#comment17206

I think this bug is not so obvious, there are two package in the same
group, one conflicts / replaces / provides the other.
There are at least 3 cases to consider here for the state before the
installation : none of the packages are installed, old package is
installed, new package is installed.
Should pacman always choose the package replacing the other ?

And what should happen without the replace flag, if the package only
provides and conflicts with the other ?