Use 0, rather that 0xffffffff, as the "no reply frame number known yet"

Use 0, rather that 0xffffffff, as the "no reply frame number known yet"
- frame numbers are 1-origin, so 0 can be used as an "exception" value.

In the protocol tree for a reply, don't say that the reply is to frame
N, just say that it's to a request starting in frame N - a frame can
contain more than one request, and a request may take more than one
frame.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@2360 f5534014-38df-0310-8fa8-9805f1628bb7