Increase the number of available loop index vars

[ToddFincannon]

Some very complex formulae in EPS use as many as 10 marked dimensions in SUM terms. Each of these needs a loop index variable. Previously, we only allocated two such variables for marked dimensions: [v, w]. We need to increase this to at least 10. At the same time, we need to prepare for subscripted variables with more than three dimensions in EPS. The loop index vars for dimensions are taken from a separate list, currently [i, j, k].

[ToddFincannon]

Hewing to mathematical convention, assign [i, j, k, l, m] to dimension loop index vars. Use the remaining letters except a-e, n, and x-z for array loop index vars. (Array and dimension loop index vars must be distinct, because array functions are sometimes evaluated over a number of dimension subscripts.) That leaves us with [u, v, w, s, t, f, g, h, o, p, q, r]. I chose to use the more mathematically common index variables u, v, w first, and then the rest in somewhat descending order of conventional use.