[dev] cal -5 and -7

[Antoni V.]

I wanted to add -5 and -7 to cal and I did.
And it works.
But it looks bad.
Can anyone think of better implementation?
Thanks.

+        case '5':
+                nmons = 5;
+                if (--month == 0) {
+                        month = 12;
+                        year--;
+                }
+                if (--month == -1) {
+                        month = 11;
+                        year--;
+                }
+                break;
+        case '7':
+                nmons = 7;
+                if (--month == 0) {
+                        month = 12;
+                        year--;
+                }
+                if (--month == -1) {
+                        month = 11;
+                        year--;
+                }
+                if (--month == -2) {
+                        month = 10;
+                        year--;
+                }
+                break;