Bigger code fragment dump on runtime errors.

I was noticing that each and every time I was trying to use the
code fragment dump that comes from runtime errors, it was never
long enough to tell me anything and I always had to increase this number.
Then I'd set it back to 4 again before checking in because it was never
part of the actual change the pull request was for.

Finally I got tired of this and made it a seperate pull request to dump
more of the program opcodes around the error.  Clearly in practice, 4 was
never enough to diagnose anything.