rebase: add documentation and test for --no-rebase-merges
As far as I can tell, --no-rebase-merges has always worked, but has never been documented. It is especially important to document it before a rebase.rebaseMerges option is introduced so that users know how to override the config option on the command line. It's also important to clarify that --rebase-merges without an argument is not the same as --no-rebase-merges and not passing --rebase-merges is not the same as passing --rebase-merges=no-rebase-cousins. A test case is necessary to make sure that --no-rebase-merges keeps working after its code is refactored in the following patches of this series. The test case is a little contrived: It's unlikely that a user would type both --rebase-merges and --no-rebase-merges at the same time. However, if an alias is defined which includes --rebase-merges, the user might decide to add --no-rebase-merges to countermand that part of the alias but leave alone other flags set by the alias. Signed-off-by: Alex Henrie <alexhenrie24@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>