Make "Dnn" and "Tnn" match case-insensitively in the "attach" dialog

Summary: These patterns are hard-coded, allow them to match case-insenstiviely.

Test Plan: Typed "d3" and "D3", got the right object in the attach dialog.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1253

Differential Revision: https://secure.phabricator.com/D2511