Redo sbatch's script reading and verification code:

morrone:/tmp$ echo | sbatch
sbatch: error: Batch script contains only whitespace!
morrone:/tmp$ echo -n | sbatch
sbatch: error: Batch script is empty!
morrone:/tmp$ echo foobar |sbatch
sbatch: error: This does not look like a batch script.  The first
sbatch: error: line must start with #! followed by the path to an interpreter.
sbatch: error: For instance: #!/bin/sh