Core3.1.5 - second try

All the tests should now display on core3.1.5 (from distro 1.3.2) as expected/documented.

(the basic auto-loader in TAP is still not functional, sry)

Many cores later... (since first release)

And the BASIC loader is still not functional... run tests manually (or use some script if running the emulator on PC).

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EDIT - by testing on my own Next with core3.1.5 and current gitlab image of "distro" there are some more tests failing/displaying differently than they were supposed to.

Some of the clashing between tests and NextZXOS should be resolved now in github, but some issues need more investigation and research (not NextZXOS related and not so easy to fix/avoid).

I.e. expect second "core3.1.5" release of the test suite (in some unspecified future), this time hopefully fully working as intended.