unit test that positive and negative selections can not be mixed

[holgerbrandl]

See
https://github.com/holgerbrandl/kscript-support-api/blob/1ecbdeecaa68d57a8b2365a42995d7ce3bee28a0/src/main/kotlin/kscript/text/Tables.kt#L111

Should be xor!?

[holgerbrandl]

Fixed in master