added (1) decoding only section (bool onlySections), (2) PartOfPacket::decode() only on demand (3) ByteStream(ByteStreamPtr b0, dword start, dword end, bool memory_sharing)

getNumberOfTypes and SDFRBlock::getBBlock().

This commit allows the application
to easily traverse the layout 4 format.

Some changes to File::fsize() and open

This reverts commit b44aff88.