[Ifeffit] max number of restraints

[Matt Newville]

Hi Victor,

It should be
  restraint_sum = restraint1 + restraint2 + restraint3 + ...

That is, a restraint should be a value that you'd like to me made as
small as possible, but can take either sign.  The restraints are
simply appended to the "vector to be minimized" in the least squares
sense.

I'm not sure that will fully solve the issue of having different
results between 10+ individual restraints and fewer summed restraints.
   But I'm interested to hear and see more....

--Matt