some syntax errors are valid

This was previously considered invalid:

fisakytt@test13nqe1-re0.dk# set c
error: syntax error: c

It should be considred valid, this change made discovery take longer, as there
are quite few of them, but more hidden commands are found

+ bugfix where we didn't wait for prompt after starting shell, thanks to @jalmargyy for spotting
+ interfaces support (interfaces is quite special, as mostly anything is valid interfaces name or may be, so few reserved words)
bump up gemspec