#5 support cluster keyword in beta spec

[Paul Williams]

* The GWC2 beta supports the new
"cluster=[keywords]" parameter. This functionality is
currently for testing of this feature, so consider it
"alpha".
* On update requests, if you include the extra
parameter "cluster=keyword1,keyword2,...", these
keywords will be stored along with the host you submit.
* The following limitations are placed on the
keyword string: it may only contain the characters
[A-Za-z0-9.-_:], and it may not be longer than 256
characters (yes, the entire keyword string). -
Characters that aren't allowed are stripped and any
keywords beyond the 256 characters are dropped.
* On get requests, the keywords are returned in the
field after the age parameter, like so:
o H|127.0.0.2:321|400|keyword1,keyword2,...

[Joe Julian]

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Requires database change. Next Major release.

[Joe Julian]

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Avancier: Do you want to tackle this one?