Increase result set to 100 from 25 for "attach" dialog

Summary: See T1254, until this gets paginated properly we can at least show more results. 25 is pretty anemic.

Test Plan: Tweaked limit, verified result count was affected.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1254

Differential Revision: https://secure.phabricator.com/D2513