Earlier, to countermand the implicit "-m" option when the
"--first-parent" option is used with "git log", we added the
"--[no-]diff-merges" option in the jk/log-fp-implies-m topic. To
leave the door open to allow the "--diff-merges" option to take
values that instructs how patches for merge commits should be
computed (e.g. "cc"? "-p against first parent?"), redefine
"--diff-merges" to take non-optional value, and implement "off"
that means the same thing as "--no-diff-merges".
* so/log-diff-merges-opt:
t/t4013: add test for --diff-merges=off
doc/git-log: describe --diff-merges=off
revision: change "--diff-merges" option to require parameter
a555b514cd