Add variable errnosave for storing the actual I/O function's errno.
Fixed error condition test for fread/fwrite.
Removed usage of ftell for fread and fwrite as it does not work on PIPEs
and the like (e.g. stdout/stderr).
Added *64 functions:
open64
creat64
pwrite64
pread64
pwritev64
preadv64
mmap64
fopen64