Fix #write_pointer when writing large value.
Fix #write_pointer when writing large value.

Error: `write_pointer': integer 10000000000 too big to convert to `int' (RangeError)

The max value of Fixnum is now based on the _long_ type, at least the case for MRI Ruby.

Signed-off-by: Shin Yee <bd076606b461da0ed9365f65e4798f407bf12faa@speedgocomputing.com>

majioa/ffi,majioa/ffi,yghannam/ffi,sparkchaser/ffi,ffi/ffi,sparkchaser/ffi,mvz/ffi,yghannam/ffi,tduehr/ffi,MikaelSmith/ffi,ferventcoder/ffi,tduehr/ffi,yghannam/ffi,majioa/ffi,tduehr/ffi,MikaelSmith/ffi,sparkchaser/ffi,yghannam/ffi,tduehr/ffi,majioa/ffi,MikaelSmith/ffi,mvz/ffi,ffi/ffi,ferventcoder/ffi,ferventcoder/ffi,yghannam/ffi,mvz/ffi,ferventcoder/ffi,mvz/ffi,sparkchaser/ffi,ffi/ffi,MikaelSmith/ffi