Turn on the fast-vector-highlighter.

So turning on the fast-vector-highlighter should fix two problems:
1.  If the text of an article is large sometimes the best highlight
isn't show.
2.  Sometimes the summary of an article is huge (Bug 52680.)

This should also speed up highlighting, especially for large articles.

The fast-vector-highlighter is engaged by storing term vectors with
positions and offsets which is what this commit actually does.

Change-Id: Ic92bf03af9f2c1851f21c2adad94d7d463ab57b5
Merge "Turn on the fast-vector-highlighter."