[Propel1] Fixed preferred choices in the ModelChoiceList.

For some reason this change was not merged from 2.1 branch.
merged branch jakzal/propel1-modelchoice-preferred-fix (PR #6569)

This PR was merged into the master branch.

Commits
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310f691 [Propel1] Fixed preferred choices in the ModelChoiceList.

Discussion
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[Propel1] Fixed preferred choices in the ModelChoiceList

Related change was made in #6454 but for some reason part of that change was not merged from 2.1 branch.

Bug fix: yes
Feature addition: no
Backwards compatibility break: no
Symfony2 tests pass: some Locale tests fail, fixed in #6568
Fixes the following tickets:
Todo: -
License of the code: MIT
Documentation PR: -