ZF/intr_elim/elim_rls: now includes Pair_inject, since coinductive definitions may involve ordinary pairs. (HOL/intr_elim does not require this change)

Pure/Unify/IMPROVING "CLEANING" OF FLEX-FLEX PAIRS: Old code would refuse to simplfy %x y.?a(x) =?= %x y.?b(f(?c(y), y)) because it found the flexible path to y before the rigid path. New code simplifies this to %x.?a(x) =?= %x.?d, eliminating ?a. Pure/Unify/rigid_bound: preliminary check for rigid paths to the banned bound variables Pure/Unify/change_bnos: any occurrences of the banned bound variables must now be flexible, causing abandonment of the "cleaning"

LK/hardquant/37: deleted call to flexflex_tac: no longer needed