fix basering change in algebra::is_injective
Merge branch 'fix.baseringchange.algebra.is_injective' of https://github.com/surface-smoothers/Sources into surface-smoothers-fix.baseringchange.algebra.is_injective

Conflicts:
	Tst/Short.lst
Merge branch 'surface-smoothers-fix.baseringchange.algebra.is_injective' into spielwiese