Tracebacks get confusing when an error happens outside docstring

[freider]

If an exception is raised by code in the same file but outside of a docstring (e.g. calling a function that's defined in the same file), the traceback gets confusing and states "code block line XX*" and can for some reason not necessarily extract the correct line (or any line) to display in the traceback.

One possible fix could be to offset the docstring tests similarly to how they are offset in the source file before eval-running them, by inserting a bunch of blank newlines before them. I think that would let us use the default traceback extraction code or at least use the source file as is for the source of truth for source code extraction

[freider]

Even more confusing: if there are lines within such a traceback that originating in other files, they also get incorrect line numbers...

[freider]

Fix for the most urgent part of this (crash in traceback generation): #37