Modify @Condition for detecting existing message bundle resource

The problem with the old code is that it worces a ResourceBundle to
initialize with the default encoding (and that is then cached in the
JDK) during @Condition evaluation (so before the encoding is known).

Includes test for swedish messages

Fixes gh-1228

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/MessageSourceAutoConfigurationTests.java

@@ -58,6 +58,18 @@ public class MessageSourceAutoConfigurationTests {
 				this.context.getMessage("foo", null, "Foo message", Locale.UK));
 	}
 
+	@Test
+	public void testEncodingWorks() throws Exception {
+		this.context = new AnnotationConfigApplicationContext();
+		EnvironmentTestUtils.addEnvironment(this.context,
+				"spring.messages.basename:test/swedish");
+		this.context.register(MessageSourceAutoConfiguration.class,
+				PropertyPlaceholderAutoConfiguration.class);
+		this.context.refresh();
+		assertEquals("Some text with some swedish öäå!",
+				this.context.getMessage("foo", null, "Foo message", Locale.UK));
+	}
+
 	@Test
 	public void testMultipleMessageSourceCreated() throws Exception {
 		this.context = new AnnotationConfigApplicationContext();

spring-boot-autoconfigure/src/test/resources/test/swedish.properties

@@ -0,0 +1 @@
+foo=Some text with some swedish öäå!