Fix ViewString for string to correctly escape characters needing it

[ChrisJefferson]

Fixes #2884

This fixes ViewString not correctly escaping strings. This is done by making the function which prints strings to the terminal generic, so we can print a string (with escape characters) to a buffer.

Note that, to make the kernel level stuff easier, I print to a plist of strings which have to be concatenated together, which then actually gets done back at the GAP level. If this offends anyone I could make a growing string and do this in one go, but this seemed easier.

[coveralls]

Coverage increased (+0.03%) to 84.508% when pulling 95e88be on ChrisJefferson:viewstring into 2c596b3 on gap-system:master.

[fingolfin]

What I don't understand: Why not instead provide a function VIEW_STRING_FOR_STRING which returns the already concatenated result? Do you have any applications in mind where one would need these separate "chunks"?

[ChrisJefferson]

Nope, just generally trying to make the C-level code as simple as possible

[fingolfin]

Seems this needs to be rebased now, too. Also, labels need to be set (at the very least a "release notes" label)

[fingolfin]

@ChrisJefferson I updated my commit to fix a comment; otherwise, this is ready to merge from my POV, but since I modified your PR, I do not want to merge this w/o your explicit approval (in particular, if you do not approve, then I don't want to merge it).

[ChrisJefferson]

Sorry, I was ignoring it while the tests still failed, but I notice this is just jenkins/gap-system being badly behaved. I'm happy with this.