Fixed wrong type declaration 

Slow fallback implementation a little bit less slow...
Array c in convolve and convolve_adjoint methods were declared as Complex (type of f/fHat) but casted to int.
Fixed int -> Int64 as Int64 are used everywhere else. Might not be wished.
TODO: 
    - the use of ellipsis seems to make Julia's code very slow. Maybe one could use code generation via macros.
    - ind2sub is not very fast.