Highlight the correct line for runtime errors in wrapped code

[sapi]

The line number of runtime errors is extracted in TestResult._addResult and used to indicate which line, if any, should be highlighted for a particular test.

In the case of compile errors, this is achieved directly in the run_test function.

The latter function has access to whether the student code has been wrapped or not, and if so, how many lines of padding were added at the top of the file. The former does not; it is far too deep in the testing hierarchy to know that.

As a result, the incorrect line is highlighted for runtime errors in wrapped code. At the moment, this means they are off by one (but that could change if the wrapping changes).

Because the code is being execed, we don't have access to the actual source of the error line, meaning we can't match on that. Using a global would be possible, but for now I'd rather have the error than complicate the framework in that way.