Reporting correct compressed/uncompressed file sizes for zip64

[ls-urs-keller]

I'm stream-uncompressing files around 1.6GB compressed, 11 GB uncompressed.
The file size is incorrectly read from zip64 file entry.

Everything works fine until at the very end when reading the stream it compares uncompressed size with the size actually read and throws an exception.

The left shift operator << seems to be the culprit e.g.:
10<<8<<8<<8<<8 = 0
whereas
10256256256256 = 42949672960

[JMS-1]

I would suggest to fix readInt (with * 256) instead of introducing a new function readLong. JavaScript makes no difference at all (as far as I understand there is no integral number representation).

And I would REALLY like this push request to be merged into the package! Actually ist starts crashing at 2GB! See #777. Although I start wondering if jszip is still maintained at all.

[ls-urs-keller]

Closing in favor of #791