Fix crazy load times for DiffSet admin page loads.

Review Request #7870 — Created Jan. 15, 2016 and submitted — Latest diff uploaded

Information

Review Board
release-2.5.x

Reviewers

The legacy_diff_hash and legacy_parent_diff_hash fields in the FileDiff
inlines for the DiffSet admin pages were loading as <select> fields, which
hammered the database and took a long time. These should be raw ID fields
instead.

Looked at a DiffSet in the admin and saw it load very quickly.