t3422: new testcases for checking when incompatible options passed

t3422: new testcases for checking when incompatible options passed

git rebase is split into three types: am, merge, and interactive.  Various
options imply different types, and which mode we are using determine which
sub-script (git-rebase--$type) is executed to finish the work.  Not all
options work with all types, so add tests for combinations where we expect
to receive an error rather than having options be silently ignored.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>