Two reasons for this:
- more fine-grained space/functionality tradeoff
- preparation for the sage 8.6 update, which finally doesn't need a
downgraded gap anymore but does break when unexpected (non-standard)
packages are installed. Details: https://trac.sagemath.org/ticket/26983
The proper way to deal with gap packages would be to create a package
set, package each one individually and have something like gap
equivalent of `python.withPackages`. I am not willing to do that
however.
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