Specify R(0) for R(n) = -1, n < startIndex

[robert-7]

Tanny -related to the point above, sometimes it is handy to be able to specify R(0) independently of whether or not we define R(n) for n<0. And if we do need to define both R(0) and R(n) for n<0 we may want to allow different values, for example, R(0)=0 and R(n) = -1 for n<0.

[robert-7]

This was fixed with commit labelled "Fixes #17". It was a mistake.