Fix property source for decrypted variables

Use SystemEnvironmentPropertySource so that env vars can be
encrypted as well as property values (i.e. FOO_BAR will bind to
@Value("foo.bar")).

Fixes gh-89, fixes gh-87

spring-cloud-context/src/test/java/org/springframework/cloud/bootstrap/encrypt/EnvironmentDecryptApplicationInitializerTests.java

@@ -30,7 +30,7 @@ import static org.junit.Assert.assertEquals;
  * @author Dave Syer
  *
  */
-public class EnvironmentDecryptApplicationListenerTests {
+public class EnvironmentDecryptApplicationInitializerTests {
 
 	private EnvironmentDecryptApplicationInitializer listener = new EnvironmentDecryptApplicationInitializer(
 			Encryptors.noOpText());
@@ -43,6 +43,14 @@ public class EnvironmentDecryptApplicationListenerTests {
 		assertEquals("bar", context.getEnvironment().getProperty("foo"));
 	}
 
+	@Test
+	public void relaxedBinding() {
+		ConfigurableApplicationContext context = new AnnotationConfigApplicationContext();
+		EnvironmentTestUtils.addEnvironment(context, "FOO_TEXT: {cipher}bar");
+		this.listener.initialize(context);
+		assertEquals("bar", context.getEnvironment().getProperty("foo.text"));
+	}
+
 	@Test
 	public void propertySourcesOrderedCorrectly() {
 		ConfigurableApplicationContext context = new AnnotationConfigApplicationContext();