We first implement new options as exact synonyms for their original
counterparts, to get all the infrastructure right, and keep functional
improvements for later commits.

The following values are implemented:

--diff-merges=          old equivalent
first|first-parent    = --first-parent (only format implications)
sep|separate          = -m
comb|combined         = -c
dense| dense-combined = --cc

Signed-off-by: Sergey Organov <redacted>
---
 diff-merges.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/diff-merges.c b/diff-merges.c
index 6446e2093661..cba391604ac7 100644
--- a/diff-merges.c
+++ b/diff-merges.c

@@ -15,6 +15,11 @@ static void set_separate(struct rev_info *revs) {
        revs->separate_merges = 1;
 }

+static void set_first_parent(struct rev_info *revs) {
+       set_separate(revs);
+       revs->first_parent_merges = 1;
+}
+
 static void set_m(struct rev_info *revs) {
        /*
         * To "diff-index", "-m" means "match missing", and to the "log"

@@ -38,11 +43,19 @@ static void set_dense_combined(struct rev_info *revs) {
 }

 static void set_diff_merges(struct rev_info *revs, const char *optarg) {
-       if (!strcmp(optarg, "off")) {
+       if (0) ;