MKID_BE relied on unspecified behavior of the C++ compiler,
and as such was always a bit unsafe. The new MKTAG macro
is slightly less elegant, but does no longer depend on the
behavior of the compiler.
Inspired by FFmpeg, which has an almost identical macro.
This should not cause any code behavior changes at this time, but if any
of the intermediate VideoDecoder classes ever starts to overload stuff,
this would become important.
svn-id: r55841
