!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

sys-libs/readline:0

  ('ebuild', '/', 'sys-libs/readline-5.2_p13', 'merge') pulled in by
    =sys-libs/readline-5* required by ('ebuild', '/', 'dev-lang/ghc-6.8.2', 'merge')
    (and 22 more)

  ('installed', '/', 'sys-libs/readline-6.0_p3', 'nomerge') pulled in by
    sys-libs/readline required by world
    sys-libs/readline required by system
    >=sys-libs/readline-4.1 required by ('installed', '/', 'dev-db/unixODBC-2.2.12', 'nomerge')
    (and 19 more)


It may be possible to solve this problem by using package.mask to
prevent one of those packages from being selected. However, it is also
possible that conflicting dependencies exist such that they are
impossible to satisfy simultaneously. If such a conflict exists in the
dependencies of two different packages, then those packages can not be
installed simultaneously.

For more information, see MASKED PACKAGES section in the emerge man page
or refer to the Gentoo Handbook.