Remove all Context.Global* methods

and change the behavior of the non-Global variants to always search up the
context lineage.

Closes #385

altsrc/helpers_test.go

@@ -1,13 +1,23 @@
 package altsrc
 
 import (
+	"os"
 	"reflect"
+	"runtime"
+	"strings"
 	"testing"
 )
 
+var (
+	wd, _ = os.Getwd()
+)
+
 func expect(t *testing.T, a interface{}, b interface{}) {
-	if !reflect.DeepEqual(b, a) {
-		t.Errorf("Expected %#v (type %v) - Got %#v (type %v)", b, reflect.TypeOf(b), a, reflect.TypeOf(a))
+	_, fn, line, _ := runtime.Caller(1)
+	fn = strings.Replace(fn, wd+"/", "", -1)
+
+	if !reflect.DeepEqual(a, b) {
+		t.Errorf("(%s:%d) Expected %v (type %v) - Got %v (type %v)", fn, line, b, reflect.TypeOf(b), a, reflect.TypeOf(a))
 	}
 }