Line number always takes precendence when running with filters.

This behaviour is strictly better than what we have now, though isn't as complete as @dchelimsky and @cupakromer envisioned in #779: if you specify a line number, it throws away all other filters. 90% of the time this is what you want ... running a context by line number and also wanting other filters applied isn't useful that often. I'm not sure how to do the latter yet.

With my current understanding, I consider the current behaviour broken, the behaviour in this PR correct, and the further proposed changes an extra enhancement.

@dchelimsky @myronmarston @cupakromer