merge: shortcircuit filemerge for identical files
- use filectx.cmp to compare files
- move merge messages into filemerge
- kill the redundant resolving message
- update tests
=======================
Should display 'First commit message'
description:
First commit message
=======================
Should display 'Second commit message'
description:
Second commit message
=======================
Should display 'Third commit message\n This is the 3rd log message'
description:
Third commit message
This is the 3rd log message
=======================
Should display 'Fifth commit message\n This is the 5th log message'
description:
Fifth commit message