Merge pull request android-async-http#560 from ebuildy/patch-1

Add "has" method, to check parameter existence.

Author: smarek

library/src/main/java/com/loopj/android/http/RequestParams.java

@@ -326,6 +326,19 @@ public void remove(String key) {
         urlParamsWithObjects.remove(key);
     }
 
+    /**
+     * Check if a parameter is defined.
+     *
+     * @param key the key name for the parameter to check existence.
+     * @return Boolean
+     */
+    public boolean has(String key) {
+        return urlParams.get(key) != null ||
+        streamParams.get(key) != null ||
+        fileParams.get(key) != null ||
+        urlParamsWithObjects.get(key) != null;
+    }
+
     @Override
     public String toString() {
         StringBuilder result = new StringBuilder();