psuh: add a built-in by popular demand

Internal metrics indicate this is a command many users expect to be
present. So here's an implementation to help drive customer
satisfaction and engagement: a pony which doubtfully greets the user,
or, a Pony Saying "Um, Hello" (PSUH).

This commit message is intentionally formatted to 72 columns per line,
starts with a single line as "commit message subject" that is written as
if to command the codebase to do something (add this, teach a command
that). The body of the message is designed to add information about the
commit that is not readily deduced from reading the associated diff,
such as answering the question "why?".

Signed-off-by: Long Nguyen <n.h.long.9697@gmail.com>

Author: nhlong9697

.gitignore

@@ -126,6 +126,7 @@
 /git-prune-packed
 /git-pull
 /git-push
+/git-psuh
 /git-quiltimport
 /git-range-diff
 /git-read-tree

Makefile

@@ -1459,6 +1459,7 @@ BUILTIN_OBJS += builtin/patch-id.o
 BUILTIN_OBJS += builtin/prune-packed.o
 BUILTIN_OBJS += builtin/prune.o
 BUILTIN_OBJS += builtin/pull.o
+BUILTIN_OBJS += builtin/psuh.o
 BUILTIN_OBJS += builtin/push.o
 BUILTIN_OBJS += builtin/range-diff.o
 BUILTIN_OBJS += builtin/read-tree.o

builtin.h

@@ -282,5 +282,6 @@ int cmd_verify_pack(int argc, const char **argv, const char *prefix, struct repo
 int cmd_show_ref(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_pack_refs(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_replace(int argc, const char **argv, const char *prefix, struct repository *repo);
+int cmd_psuh(int argc, const char **argv, const char *prefix, struct repository *repo);
 
 #endif

builtin/psuh.c

@@ -0,0 +1,8 @@
+#include "builtin.h"
+#include "gettext.h"
+
+int cmd_psuh(int argc UNUSED, const char **argv UNUSED,
+	const char *prefix UNUSED, struct repository *repo UNUSED) {
+    printf(_("Pony saying hello goes here.\n"));
+    return 0;
+}

git.c

@@ -627,6 +627,7 @@ static struct cmd_struct commands[] = {
 	{ "prune-packed", cmd_prune_packed, RUN_SETUP },
 	{ "pull", cmd_pull, RUN_SETUP | NEED_WORK_TREE },
 	{ "push", cmd_push, RUN_SETUP },
+	{ "psuh", cmd_psuh, RUN_SETUP },
 	{ "range-diff", cmd_range_diff, RUN_SETUP | USE_PAGER },
 	{ "read-tree", cmd_read_tree, RUN_SETUP },
 	{ "rebase", cmd_rebase, RUN_SETUP | NEED_WORK_TREE },