Simplify general_ functions handling of inplace transforms

A bit of cleanup in general_c, general_dcst and general_r for code handling in-place transforms.

Very nice, thanks a lot!

(And, BTW, thanks as well for putting up with my weird indentation style... I know it must feel horrible for anyone but me, and I try to get rid of it, but never really managed so far..)

merged

mentioned in commit d72f8ade