Make the bytes-written information from Wiretap a long, as we allow

Make the bytes-written information from Wiretap a long, as we allow
files to get that big.

From Thomas Wittwer and Matthias Nyffenegger:

Support for "ring buffer mode", wherein there's a ring buffer of N
capture files; as each capture file reaches its maximum size (the ring
buffer works only with a maximum capture file size specified), Ethereal
rolls over to the next capture file in the ring buffer, replacing
whatever packets might be in it with new packets.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@4324 f5534014-38df-0310-8fa8-9805f1628bb7