Simplify DifferentialHunk::getAddedLines()
Summary: I will also need getRemovedLines() so refactor this first.
Test Plan:
New test case.
Viewed uncached diff.
Verified that the only callsite of getAddedLines() trims lines.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D2875