Support nontrivial GAP input

[nathancarter]

I have not yet tested this change; I'm submitting it just to ask if something this straightforward could solve the issue in this post (which Andrey has been kind enough to ask on my behalf). I tried to test this with a docker container of SageMathCell but the one I found was not functioning. If you'd like to test this, or teach me how to test it, that could be good. Or this can be the start of a discussion.

[novoselt]

Have you tried to follow instructions on the main page here to install SageMathCell for development? Assuming that you have Sage itself installed, it should be relatively fast and easy.

Regarding the fix itself - I am not in favour of merging it since it is a workaround for this particular code, but files are used for a reason, so for something else things may break. So I'd rather try to do something in Sage itself, even if not using files by default is the way to do. We should also see how well libgap is in executing GAP commands (they have to be fed one by one, so one has to split the code first). Perhaps we should just use that one.