graft-state: save --base in graft's state, fixing bug with graft --continue
Without this change, running graft --continue after grafting a merge commit using --base
(and encountering conflicts) will output "skipping ungraftable merge revision" even though
we specified a base in the initial graft command.
Graft's improve behaviour is reflected in test-graft.t.
Differential Revision: https://phab.mercurial-scm.org/D8578
$ hg init
$ echo a > a
$ hg ci -Am t
adding a
$ hg mv a b
$ hg ci -Am t1
$ hg debugrename b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
$ hg mv b a
$ hg ci -Am t2
$ hg debugrename a
a renamed from b:37d9b5d994eab34eda9c16b195ace52c7b129980
$ hg debugrename --rev 1 b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3