Merge branch 'rl/show-empty-prefix' into maint

Unlike "git rev-parse --show-cdup", "--show-prefix" did not give an
empty line when run at the top of the working tree.

By Ross Lagerwall
* rl/show-empty-prefix:
  rev-parse --show-prefix: add in trailing newline

builtin/rev-parse.c

@@ -634,6 +634,8 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 			if (!strcmp(arg, "--show-prefix")) {
 				if (prefix)
 					puts(prefix);
+				else
+					putchar('\n');
 				continue;
 			}
 			if (!strcmp(arg, "--show-cdup")) {