Trim the Domain Name from cached image references

This commit removes the Domain Name, if any, from the cached image
reference before computing the image fingerprint. This way the same
image, if stored in some oter mirror, is still seen as the same one.

Fixes #158

vendor/github.com/asaskevich/govalidator/arrays.go

@@ -9,6 +9,35 @@ type ResultIterator func(interface{}, int) interface{}
 // ConditionIterator is the function that accepts element of slice/array and its index and returns boolean
 type ConditionIterator func(interface{}, int) bool
 
+// ReduceIterator is the function that accepts two element of slice/array and returns result of merging those values
+type ReduceIterator func(interface{}, interface{}) interface{}
+
+// Some validates that any item of array corresponds to ConditionIterator. Returns boolean.
+func Some(array []interface{}, iterator ConditionIterator) bool {
+	res := false
+	for index, data := range array {
+		res = res || iterator(data, index)
+	}
+	return res
+}
+
+// Every validates that every item of array corresponds to ConditionIterator. Returns boolean.
+func Every(array []interface{}, iterator ConditionIterator) bool {
+	res := true
+	for index, data := range array {
+		res = res && iterator(data, index)
+	}
+	return res
+}
+
+// Reduce boils down a list of values into a single value by ReduceIterator
+func Reduce(array []interface{}, iterator ReduceIterator, initialValue interface{}) interface{} {
+	for _, data := range array {
+		initialValue = iterator(initialValue, data)
+	}
+	return initialValue
+}
+
 // Each iterates over the slice and apply Iterator to every item
 func Each(array []interface{}, iterator Iterator) {
 	for index, data := range array {