TestSuite output:

    $ phpunit test/testsuite/misc/MoreRelationTest.php
    PHPUnit 3.7.13 by Sebastian Bergmann.

    Configuration read from /Users/marc/Propel/phpunit.xml.dist

    F

    Time: 0 seconds, Memory: 18.75Mb

    There was 1 failure:

    1) MoreRelationTest::testContentsDeletion
    We assigned a collection of only one item.
    Failed asserting that 4 matches expected 1.

    /Users/marc/Propel/test/testsuite/misc/MoreRelationTest.php:97

    FAILURES!
    Tests: 1, Assertions: 2, Failures: 1.

Added a test set that proves the bug.

…ryKeys` at class ForeignKey

and use it in the PHP5ObjectBuilder to check whether we have to backup the data of the relation entries
to be able to manipulate it later.
Added these methods because `isForeignPrimaryKey` returns only true if _all_ foreign columns are pks,
which is not useful in this case.

… proves that 'onDelete=setnull' works, too.