Accept all media types in StringDecodere

This commit adds the "*/*" media type in the list of compatible media
types for the StringDecoder. This allows this decoder to decoder
payloads of any media type as long as the target type is String.

Fixes #87

spring-web-reactive/src/main/java/org/springframework/core/codec/support/StringDecoder.java

@@ -25,6 +25,7 @@ import reactor.core.publisher.Flux;
 import org.springframework.core.ResolvableType;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.util.MimeType;
+import org.springframework.util.MimeTypeUtils;
 
 /**
  * Decode from a bytes stream to a String stream.
@@ -63,7 +64,7 @@ public class StringDecoder extends AbstractDecoder<String> {
 	 * and decode a single consolidated String or re-emit items as they are provided
 	 */
 	public StringDecoder(boolean reduceToSingleBuffer) {
-		super(new MimeType("text", "*", DEFAULT_CHARSET));
+		super(new MimeType("text", "*", DEFAULT_CHARSET), MimeTypeUtils.ALL);
 		this.reduceToSingleBuffer = reduceToSingleBuffer;
 	}