Smarter line clipping in Find in Files

For #9659 (at least part of it).
Best to explain with a before/after:
__Before__:
![image](https://cloud.githubusercontent.com/assets/2641501/4835524/5ab1b45a-5fb8-11e4-936c-e23613aa3aea.png)

__After__:
![image](https://cloud.githubusercontent.com/assets/2641501/4835529/60a1803e-5fb8-11e4-8ab6-1eed3650db9b.png)

So there are three ways text can clip:
* If endCh (last char of match) is < 200, the line is simply displayed and clipped after 200 chars
* If the match is longer than 200 chars, the match is displayed, highlighted and clipped after 200 chars (_may not be perfect_, but you'll probably only get into this state with RegExps)
* Else, the code tries to center the match in the displayed line (and, of course, it highlights the match)