jump calls can crash the MTS engine

[mezzodrinker]

The following code example will crash the engine:

function Foo()

jump Bar;

end

label Start

Foo();

end

label Bar

end

It crashes because the engine has to terminate after executing the label Bar which is called by jump from inside a function. The same would happen if you try to use jump in a label called by the command

call Label;

[mezzodrinker]

Edited code formatting

[Chimaine]

Do not pop the top frame on JumpF and enter a new scope. Fixes #6

→ <<cset c5db8d7a0510>>