Update to add build contraints to not compile in yaml support

in the case the golang version is less than golang 1.2

altsrc/yaml_file_loader.go

@@ -0,0 +1,84 @@
+// Disabling building of yaml support in cases where golang is 1.0 or 1.1
+// as the encoding library is not implemented or supported.
+
+// +build !go1,!go1.1
+
+package altsrc
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"os"
+
+	"github.com/codegangsta/cli"
+
+	"gopkg.in/yaml.v2"
+)
+
+type yamlSourceContext struct {
+	FilePath string
+}
+
+// NewYamlSourceFromFile creates a new Yaml InputSourceContext from a filepath.
+func NewYamlSourceFromFile(file string) (InputSourceContext, error) {
+	ymlLoader := &yamlSourceLoader{FilePath: file}
+	var results map[string]interface{}
+	err := readCommandYaml(ysl.FilePath, &results)
+	if err != nil {
+		return fmt.Errorf("Unable to load Yaml file '%s': inner error: \n'%v'", filePath, err.Error())
+	}
+
+	return &MapInputSource{valueMap: results}, nil
+}
+
+// NewYamlSourceFromFlagFunc creates a new Yaml InputSourceContext from a provided flag name and source context.
+func NewYamlSourceFromFlagFunc(flagFileName string) func(InputSourceContext, error) {
+	return func(context cli.Context) {
+		filePath := context.String(flagFileName)
+		return NewYamlSourceFromFile(filePath)
+	}
+}
+
+func readCommandYaml(filePath string, container interface{}) (err error) {
+	b, err := loadDataFrom(filePath)
+	if err != nil {
+		return err
+	}
+
+	err = yaml.Unmarshal(b, container)
+	if err != nil {
+		return err
+	}
+
+	err = nil
+	return
+}
+
+func loadDataFrom(filePath string) ([]byte, error) {
+	u, err := url.Parse(filePath)
+	if err != nil {
+		return nil, err
+	}
+
+	if u.Host != "" { // i have a host, now do i support the scheme?
+		switch u.Scheme {
+		case "http", "https":
+			res, err := http.Get(filePath)
+			if err != nil {
+				return nil, err
+			}
+			return ioutil.ReadAll(res.Body)
+		default:
+			return nil, fmt.Errorf("scheme of %s is unsupported", filePath)
+		}
+	} else if u.Path != "" { // i dont have a host, but I have a path. I am a local file.
+		if _, notFoundFileErr := os.Stat(filePath); notFoundFileErr != nil {
+			return nil, fmt.Errorf("Cannot read from file: '%s' because it does not exist.", filePath)
+		}
+		return ioutil.ReadFile(filePath)
+	} else {
+		return nil, fmt.Errorf("unable to determine how to load from path %s", filePath)
+	}
+}