propelorm/Propel — pull request #420 by havvg (2012-07-19 10:11:19+00:00)
Title: allow chaining of keyColumns in PropelObjectCollection::toKeyValue

We got the following use-case, where this is comes in very handy.

We have a user profile and a list of available attributes.
The profile has a list of entries of which each relates to one attribute and a value on the respective profile.

With this patch, a call like `$this->getEntriesJoinAttribute()->toKeyValue(array('Attribute', 'Ident'), 'Value')` yields a key value for attribute identifier to value.

```
array(size=3)
'COMPANY_NAME' =>string'Ormigo GmbH'(length=11)
'FIRSTNAME' =>string'Toni'(length=4)
'PROFILE_PHOTO' =>string'c4ca4238a0b923820dcc509a6f75849b.jpeg'(length=37)
```