  We study II_1 factors M and N associated with good generalized Bernoulli
actions of groups having an infinite almost normal subgroup with the relative
property (T). We prove the following rigidity result: every finite index
M-N-bimodule (in particular, every isomorphism between M and N) is described by
a commensurability of the groups involved and a commensurability of their
actions. The fusion algebra of finite index M-M-bimodules is identified with an
extended Hecke fusion algebra, providing the first explicit computations of the
fusion algebra of a II_1 factor. We obtain in particular explicit examples of
II_1 factors with trivial fusion algebra, i.e. only having trivial finite index
subfactors.
