Adding Int64Slice related stuff in flag.go and context.go, and related tests

context.go

@@ -75,6 +75,12 @@ func (c *Context) IntSlice(name string) []int {
 	return lookupIntSlice(name, c.flagSet)
 }
 
+// Int64Slice looks up the value of a local int slice flag, returns nil if no int
+// slice flag exists
+func (c *Context) Int64Slice(name string) []int64 {
+	return lookupInt64Slice(name, c.flagSet)
+}
+
 // Generic looks up the value of a local generic flag, returns nil if no generic
 // flag exists
 func (c *Context) Generic(name string) interface{} {
@@ -160,6 +166,15 @@ func (c *Context) GlobalIntSlice(name string) []int {
 	return nil
 }
 
+// GlobalInt64Slice looks up the value of a global int slice flag, returns nil if
+// no int slice flag exists
+func (c *Context) GlobalInt64Slice(name string) []int64 {
+	if fs := lookupGlobalFlagSet(name, c); fs != nil {
+		return lookupInt64Slice(name, fs)
+	}
+	return nil
+}
+
 // GlobalGeneric looks up the value of a global generic flag, returns nil if no
 // generic flag exists
 func (c *Context) GlobalGeneric(name string) interface{} {
@@ -396,6 +411,16 @@ func lookupIntSlice(name string, set *flag.FlagSet) []int {
 	return nil
 }
 
+func lookupInt64Slice(name string, set *flag.FlagSet) []int64 {
+	f := set.Lookup(name)
+	if f != nil {
+		return (f.Value.(*Int64Slice)).Value()
+
+	}
+
+	return nil
+}
+
 func lookupGeneric(name string, set *flag.FlagSet) interface{} {
 	f := set.Lookup(name)
 	if f != nil {