New errno code interpretation and gsl-condition definitions
Make a defconstant on earmuffed symbols of cffi:defcenum gsl-errorno, e.g. +continue+, +failure+, +success+, etc., and use those in define-gsl-condition forms in condition.lisp. Remove the symbol macro definition of 'success. Define a condition 'unspecified-errno in case an error code is processed that isn't in the list. Redefine #'success-failure to true if either +success+ or +continue+, from non-negative. In roots-multi, fixed error in multiroot-test-residual return for, and changed roots-multi-example-no-derivative to insure the loop is executed at least once so that fnval and argval are always bound before exiting.
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