use escaped "Can't" constant at IssuesHelperTest

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Rails4: replace hard-coded html with class at ApplicationHelperTest#test_wiki_links_within_wiki_page_context

See r12784 comment.

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fix wrong issue 'assigned-to-my-group' css class (#16038)

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Make sure that Repository#extra_info returns a Hash or nil (#16032).

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Show tabs for existing custom field types only and adds a view for choosing the type when adding a new custom field.

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Updated locales.

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Code cleanup.

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Project.activities should always return a ActiveRecord::Relation (#15983).

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Adds JS response support to #render_error (#15760).

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