Fix a 'not a normal file' error when compressing large files.

The bzip2 command line would report 'not a normal file' for files of
size larger than 2^32 - 1 bytes.

Patch bzip2.c to use _stati64 instead of _stat so that a successful
result is returned for large files.

Resolves https://github.com/philr/bzip2-windows/issues/3.