Change keystore to version 3

* Change password protection crypto in keystore to version 3
* Update KeyStoreTests/basic_tests.json
* Add support for PBKDF2 with HMAC-SHA256
* Change MAC and encryption key to avoid unnecessary hashing
* Add tests for test vectors in new wiki page defining version 3
* Add tests for new keystore tests in ethereum/tests repo
* Move JSON loading util to common for use in both tests and
  crypto packages
* Add backwards compatibility with key store version 1

common/test_utils.go

@@ -0,0 +1,37 @@
+package common
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+)
+
+// LoadJSON reads the given file and unmarshals its content.
+func LoadJSON(file string, val interface{}) error {
+	content, err := ioutil.ReadFile(file)
+	if err != nil {
+		return err
+	}
+	if err := json.Unmarshal(content, val); err != nil {
+		if syntaxerr, ok := err.(*json.SyntaxError); ok {
+			line := findLine(content, syntaxerr.Offset)
+			return fmt.Errorf("JSON syntax error at %v:%v: %v", file, line, err)
+		}
+		return fmt.Errorf("JSON unmarshal error in %v: %v", file, err)
+	}
+	return nil
+}
+
+// findLine returns the line number for the given offset into data.
+func findLine(data []byte, offset int64) (line int) {
+	line = 1
+	for i, r := range string(data) {
+		if int64(i) >= offset {
+			return
+		}
+		if r == '\n' {
+			line++
+		}
+	}
+	return
+}