added default content type

src/main/java/org/scribe/model/Request.java

@@ -17,6 +17,8 @@ import org.scribe.utils.*;
 class Request
 {
   private static final String CONTENT_LENGTH = "Content-Length";
+  private static final String CONTENT_TYPE = "Content-Type";
+  public static final String DEFAULT_CONTENT_TYPE = "application/x-www-form-urlencoded";
 
   private String url;
   private Verb verb;
@@ -108,6 +110,12 @@ class Request
   void addBody(HttpURLConnection conn, byte[] content) throws IOException
   {
     conn.setRequestProperty(CONTENT_LENGTH, String.valueOf(content.length));
+
+    // Set default content type if none is set.
+    if (conn.getRequestProperty(CONTENT_TYPE) == null)
+    {
+      conn.setRequestProperty(CONTENT_TYPE, DEFAULT_CONTENT_TYPE);
+    }
     conn.setDoOutput(true);
     conn.getOutputStream().write(content);
   }