How does one require the seq library after installing an updated version of it with package.el?

[Clément Pit-Claudel]

Hi there,

Because package.el requires `seq', seq is loaded very early after starting 
Emacs — so early, in fact, that when package-initialize adds elpa/ directories 
to the load-path, seq is already loaded.

As a result, even if a newer version of seq is installed, it is never loaded, 
because the built-in seq library is already loaded.

I got bitten by this while developing a package that uses seq-sort-by, which 
isn't available in Emacs 25's built-in seq.  I added a dependency on seq 2.14, 
which does contain seq-sort-by, but that doesn't help: package.el does install 
the dependency, but it is never loaded.

Is this a bug, or am I doing something wrong?

Thanks!
Clément.