* DissectorTable.add does not allow to add lua protocols that don't have a dissector.

* DissectorTable.add does not allow to add lua protocols that don't have a dissector.
* ProtoFiled.uint checks the base to be a valid value to avoid an assertion in proto.c while registering the field array
* save one lua table lookup by using a reference to the dissectors table instead of looking for it by name
* set data_hanlde's value to avoid a crash while invoking it.
* make the TvbRange of Tree:add_item really optional.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@17220 f5534014-38df-0310-8fa8-9805f1628bb7