remove Rails4 deprecated Relation#all from IssueTest#test_visible_and_nested_set_scopes and add awesome_nested_set regression test

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extra : convert_revision : svn%3Ae93f8b46-1217-0410-a6f0-8f06a7374b81/trunk%4012708
add more comment about awesome_nested_set 2-1-stable branch regression

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extra : convert_revision : svn%3Ae93f8b46-1217-0410-a6f0-8f06a7374b81/trunk%4012709