For 64-bit arch, Qt defines quint64 as unsigned long long (and quint32 as unsigned int), but Protobuf's google::protobuf::uint64 is defined as unsigned long. Now Qt defines qbswap only for the Qt defined 8/16/32/64 integer types aka q[u]intXXX. So qbswap<unsigned long long> and qbswap<unsigned int> is defined but not qbswap<unsigned long>.
mld.cpp was using qToBigEndian (which uses qbswap in turn) with a protobuf uint64 triggering the undefined references on some 64bit platforms.
Fixes#265
