EOVERFLOW for ftell, ftello, fgetpos?

[Roland McGrath]

Aren't ftell, ftello, and fgetpos supposed to diagnose EOVERFLOW?
(A program could fopen, fread pieces totalling >4GB, and then call ftell.)

Right now these functions all just truncate the result of _IO_seekoff to 32
bits (and treat 4294967295 as an error).  Unless someone tells me why I'm
wrong about thinking this is a bug, I will fix them to detect overflow.