Prefix and postfix all extracted phrases when phrase is not complete [LUCENE-4441]

Heya,
I would like to be able to prefix and postfix phrases when extracted text is not a complete phrase.

For example, let's say I have a phrase like

```none

"Here is my text"
```

and another like

```none

"This is a very long text and I want that Lucene highlight it even if this content is very long."
```

When highlighting "text", I get something like:

```html

"Here is my text"
"This is a very long text and I want that Lucene highlight"
```

What I would like to get back is:

```html

"Here is my text"
"This is a very long text and I want that Lucene highlight [...]"
```

As you can see, the " [...]" is added at the end because we extracted content from the field and not all the field.

So, we can add some options to Highlighter (FastVectorHighlighter) as follow:

```java
// Default values :
// preLine = null;
// postLine = null;
public final String[] getBestFragments( final FieldQuery fieldQuery, IndexReader reader, int docId,
String fieldName, int fragCharSize, int maxNumFragments,
FragListBuilder fragListBuilder, FragmentsBuilder fragmentsBuilder,
String[] preTags, String[] postTags, String preLine, String postLine, Encoder encoder ) throws IOException;
```

I hope this is doable. :-/

---
Migrated from [LUCENE-4441](https://issues.apache.org/jira/browse/LUCENE-4441) by David Pilato (@dadoonet)

The issue names FastVectorHighlighter and its getBestFragments overload; start there and trace how extracted fragments determine whether the full field was returned. Done means the requested preLine/postLine markers appear for incomplete extracted phrases while complete-phrase behavior remains unchanged; the payload names no test file, so locate the relevant highlighter tests.

Written by the indexing model from the issue text.