Remove unnecessary casts
Some code carefully cast all data buffer arguments for BufFileWrite()
and BufFileRead() to void *, even though the arguments are already
void * (and AFAICT were never anything else). Remove this unnecessary
clutter.
Discussion:
https://www.postgresql.org/message-id/flat
Update types in File API
Make the argument types of the File API match stdio better:
- Change the data buffer to void *, from char *.
- Change FileWrite() data buffer to const on top of that.
- Change amounts to size_t, from int.
In passing, change the FilePrefetch() amount argument from int to
