t3432: test rebase fast-forward behavior

t3432: test rebase fast-forward behavior

When rebase is run on a branch that can be fast-forwarded, this should
automatically be done. Create test to ensure this behavior happens.

There are some cases that currently don't pass. The first case is where
a feature and master have diverged, running
"git rebase master... master" causes a full rebase to happen even though
a fast-forward should happen.

The second case is when we are doing "git rebase --fork-point" and a
fork-point commit is found. Once again, a full rebase happens even
though a fast-forward should happen.

Mark these cases as failure so we can fix it later.

Signed-off-by: Denton Liu <redacted>
Signed-off-by: Junio C Hamano <redacted>