Support grep's "-w" flag [PATCH]

```
It's nice to be able to search for 'whole words', which is to say making sure
the pattern has a word boundary at the beginning and end.

Having to type '\bpattern\b' is annoying, and grep/ack already have a -w flag
which does this for you.
Since we already have -i which adjusts the pattern, I think adding another one
isn't to terrible.

I've attached a patch that does this.

```

Original issue reported on code.google.com by `dgryski` on 17 Feb 2012 at 1:13

Attachments:
- [csearch-w.patch](https://storage.googleapis.com/google-code-attachments/codesearch/issue-13/comment-0/csearch-w.patch)

Überprüfe den beigefügten csearch-w.patch und die bestehende Behandlung von Befehlszeilen-Flags im codesearch-Repository. Bestätige, wie das aktuelle -i-Flag das Suchverhalten ändert, und verifiziere anschließend, dass -w die Suche nach ganzen Wörtern aktiviert und dass die relevanten Suchprüfungen erfolgreich sind.

Vom Indexierungsmodell aus dem Issue-Text verfasst.