Fixes android-async-http#61, allow removing of Basic Auth credentials

Author: smarek

library/src/com/loopj/android/http/AsyncHttpClient.java

@@ -348,6 +348,13 @@ public void setBasicAuth(String username, String password, AuthScope scope) {
         this.httpClient.getCredentialsProvider().setCredentials(scope, credentials);
     }
 
+    /**
+     * Removes set basic auth credentials
+     * */
+    public void clearBasicAuth(){
+        this.httpClient.getCredentialsProvider().clear();
+    }
+
     /**
      * Cancels any pending (or potentially active) requests associated with the
      * passed Context.