fs.read() and fs.write() can't handle more than 2GB files on 64bit platform.
Also fs.truncate() can't handle more than 4GB files.

Node already has the capability to handle large files.
This patch changes only a parameter check (read/write) and
type conversion from JS's number to C types (truncate).

The testcase only works on 64bit platform, then I put it into test/disabled.

Thanks bnoordhuis (Ben Noordhuis)