Fix principal error in makeChangesWithContext()

Summary: array_fill(), contrary to range(), doesn't accept the last element but the number of elements.

Test Plan: Reparsed commit not changed after the last diff but rebased which was previously reported as changed.

Reviewers: jungejason, epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D2783