Delete negative indices in array (fix #954)

tests/jq.test

@@ -784,6 +784,10 @@ null
 {"foo": [1,4], "bar": [1]}
 {"bar": [1]}
 
+del(.[1], .[-6], .[2], .[-3:9])
+[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+[0, 3, 5, 6, 9]
+
 #
 # Assignment
 #