REST API filtering with lists doesn't work

This ticket is a migrated Trac ticket [3413](http://trac.buildbot.net/ticket/3413)

People contributed to the original ticket: @hawkowl, @djmitche, @tardyp
Ticket created on: `Jan 18 2016`
Ticket last modified on: `Jan 21 2016`

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`builders?tags__eq=sometag` should filter for builders tagged "sometag". It doesn't.

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_Comment from_: @dustin
_Date_: `Jan 20 2016`

https://github.com/buildbot/buildbot/pull/1954

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_Comment from_: @tardyp
_Date_: `Jan 21 2016`

Please don't close yet, as we need to implement the equivalent filtering on the client, for automatic update

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_Comment from_: @dustin
_Date_: `Jan 21 2016`

OK, leaving open