You can add this module to Infinispan's repository under the root (so, a 'spring' directory alongside 'core', etc). I also think it makes sense to have this in 4.2.x and master branches.
Thoughts?
Since it's just a new module that doesn't affect the current code base
in any way I too think that it makes sense to have this in 4.2.x. Are
there any commit rules I should pay attention to? I.e. do I create this
module in 4.2.x and merge that into master? Or the other way around? How
do you usually handle this?