Added testing function for ZString.

IMFMessage.h

@@ -19,6 +19,7 @@ namespace coreutils {
       void addHeader(const char *key, ZString value);
 
       ZString getHeader(ZString key, bool valueOnly = true);
+      ZString getHeaderKeyPairValue(const char *headerKey, const char *key);
       ZString getHeaderKeyPairValue(ZString headerKey, ZString key);
 
       IMFBody * getBody();