[Cin] User Defined Blend Algebra

[Andrea paz]

I compiled without the bcast6 flag and putting your latest patch. All
OK, thank you.
I started from terminal with the two exports and everything works
fine, same as you reported. So the problem was just that flag of
./configure.

Tomorrow I'm going to do some testing, including the change you
suggested: “OK, but now you can take the arith_subtract function,
change the expression for alpha to something like A_OUT = A(s); or
even A_OUT = 1;, and you'll get green”

But first I want to fully understand how the userlib works...