Renames the bound pair of a paired abstraction, quantified term,
or other binder.
The conversion GEN_PALPHA_CONV provides alpha conversion for lambda
abstractions of the form \p.t, quantified terms of the forms !p.t,
?p.t or ?!p.t, and epsilon terms of the form @p.t.
The renaming of pairs is as described for PALPHA_CONV.
GEN_PALPHA_CONV q tm fails if q is not a variable,
or if tm does not have one of the required forms.
GEN_ALPHA_CONV q tm also fails if tm does have one of these forms,
but types of the variables p and q differ.