Passing of arguments to wrappers' blocks is limited and potentially unsafe

[martijnthe]

Right now the compiler is "fooled" into passing an array of 6 id type values when calling the wrappers' blocks.
It's better to replace this mechanism with a generic solution, e.g. using ffi_call from libffi.

See https://github.com/landonf/libffi-ios for a iOS adapted version of libffi
See also http://linux.die.net/man/3/ffi_call