sign(z) for complex z should be an error

[rtoy]

Imported from SourceForge on 2024-07-09 19:41:32
Created by macrakis on 2021-10-11 16:50:05
Original: https://sourceforge.net/p/maxima/bugs/3875

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declare(z,complex)$
sign(z) => pnz
sign(sqrt(z)) => pz

These are incorrect; they should both give an error the way sign(%i) does.

csign is correct:

declare(z,complex)$
csign(z) => complex
csign(sqrt(z)) => complex