merge: fix spurious merges for copies in linear updates
We make better use of contexts to accurately identify copies that
don't need merges.
Add a simple test and update other tests.
1:016807e6fdaf
0:eb43f19ff115
016807e6fdaf tip
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
eb43f19ff115
eb43f19ff115+
reverting file1
? file1.orig
eb43f19ff115
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
? file1.orig
016807e6fdaf tip
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
? file1.orig
016807e6fdaf tip
? file1.orig
016807e6fdaf tip
? file1.orig
016807e6fdaf tip
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
? file1.orig
016807e6fdaf tip