Jukebox radio fixes
New gun sprites
A sensor which registers mechs and trains attempting to pass by and, if necessary, blocks their movement.

If enabled, detects mechs/trains and blocks their movement if they are coming from any of the directions set by dir. Can currently only be enabled/disabled by radio command and airlocks are updated to utilize this.

The current setup allows mechs to move through airlocks during normal cycles, which for example lets Odysseus out to save lives.
Once a shuttle docks however, the sensors are enabled to prevent boarding.

If blocked, players receive a simple message stating that their command has been overridden.
Added check for blank on name entry
Since cancel just returns a blank this checks for that and doesn't raise an error.
Changes check to an isnull rather than a truth test
This allows the client to detect the difference between a blank and someone pressing cancel.
Merge pull request #324 from ZomgPonies/master

Patch