#800 Warn about genotypes with wild type endogenous allele

[Kim Rutherford]

For after release of multi-allele version:

We can add a wild type endogenous allele if there is a wild type allele of the same gene with a non-endogenous expression. But we can also then delete the non-endogenous expression allele. That should be disallowed.

See also: https://sourceforge.net/p/pombase/curation-tool/782/