Improve printing of errors when the tycons look the same

See Trac #8278.  Example new message:

    Couldn't match expected type ‛T8278a.Maybe’
                with actual type ‛Maybe a0’
    NB: ‛T8278a.Maybe’ is defined in ‛T8278a’
        ‛Maybe’ is defined in ‛Data.Maybe’ in package ‛base’
    In the first argument of ‛f’, namely ‛Nothing’

The "NB" is the new bit