r.reasenberg/d.white   jan 1974   subroutine solctl
increment normal equations with saved normal equations and solve
or restore saved solution (for maximum liklihood estimator
or kalman-bucy filter)

set icv(6) for dipsnec control from ict(76)
ict(76)= 0 no dipsnec operations
2 flag differences between adjustable nominals
4 flag differences between all nominals
6 copy nominals from imat0(1)
10+n same as n, but also correct rhs for differences