Fix for unreasonable flight times

Was caused by special packets from voxel/particle/model servers not containing flags, seq, timestamp but being parsed as if they did.

Repro: shooting a particle using gun.js will result in a ParticleErase packet being sent when the particle hits something.  This will result in "ignoring unreasonable packet... flight time: ###" on the client side.

Testing: 
- gun.js was used to send new-version ParticleErase packets with flags, seq, and timestamp added after the packet header.  It was verified that the client received these packets with correct seq and timestamp relative to other packets.  No flight-time error occurred.
- editModel.js was used to send new-version ModelErase packets when a model was deleted.  Same info was verified on the client side as the ParticleErase packet testing.
- New-version EnvironmentData packets were sent by running domain server with a config file to automatically send environment data.  Same info was verified on the client side as above.
- Non-special packets were tested by doing general tasks, such as shooting particles at voxels and moving models around.  Shot particles still moved and deleted struck voxels, and moving the models still changed their positions, indicating that non-special packets were still being parsed correctly.