Previous Merge Master Changes before Current Auto Merge should not show in Bitbucket Diff pages

[dianawang]

Master Version: older version a -->new version b

1. User create branch c from master a

2. User make some changes in branch c

3. User merge master b to branch c

4. User pull request to auto merge branch c to master

Expect differences in Bitbucket Diff page: Only user changes in step2

Actual differences in Bitbucket Diff page: Also changes made by others from a to b besides user changes in step2. This make the Diff Page a mess, not convenient to check real differences