Allow to run to empty lines or lines with comments

So, for once, I am going to request a feature without implementing it. This touches on the actual debugging code, which I feel much less comfortable hacking. Also, the way it's currently implemented, some things would have to be redisigned non-trivially. And I really do need to get back to hacking SymPy :)

Basically, it would be nice if you could run to empty lines, or lines with comments. I wouldn't mind if this was really just a shortcut for running to the next actual runnable line, or if it's at the end of a file, to just run everything _without_ giving the "Finished" dialog).

There are probably some nuances I am not considering here (e.g., could there be problems involved with return statements?). So I am going to just leave this here and hope that Andreas or someone else implements it.

The issue does not name files or tests; start by tracing the debugger's handling of run-to-line behavior and reproduce a blank or comment line case. Define and test whether stopping on such lines means moving to the next runnable line, how end-of-file handling avoids the “Finished” dialog, and whether return statements introduce problems.

Written by the indexing model from the issue text.