Merge 'exec: internal error' with ShellJSInternalError

[nfischer]

I can't actually remember why we have both ShellJSInternalError and exec: internal error, but they mean the same thing: there's a bug in ShellJS code somewhere. These should probably get merged together, so that we can actually keep the exception stack for bugs in exec. This would help immensely in debugging.

While it's true that exec() sometimes crashes unavoidably (like if we overrun the max buffer), it's definitely still helpful to have the stack trace, and it still makes sense to report it as an exception, instead of with shell.error() (that should be reserved for the external command's stderr).

[nfischer]

@freitagbr can you investigate this?

[freitagbr]

Yes, I will look into this.

[nfischer]

@freitagbr is this something we can land for v0.8.0?

[freitagbr]

Yeah, I can put something together in the next few days.

[nfischer]

I think we'll have to bump this back to v0.9.0, didn't quite sort out the PR in time.