error codes for `gsh` commands

[phyver]

It would be nice if gsh commands returned a value: 0 for OK, or some error code.

The problem is that gsh check will also do a clean and an init.

One possibility would be to have different function used different bits in the return value:

• lsb for check
• bit 1 for init
• bit 2 for test
• bit 3 for static
• bit 4 for goal
• bit 5 for treasure
• bit 6 for treasure-msg

We'll have one last bit to use for something else!

[phyver]

Simpler solution:

• no return value for gsh static and gsh init (if init returns true, the mission is skipped anyway).
• 0/1 return value for gsh check and gsh test
• 0/1 return value for gsh goal