Bugfix - plib support would not compile anymore.

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/trunk/supertuxkart@1496 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/sound_plib.cpp

@@ -55,7 +55,7 @@ void MusicPlib::update()
 }
 
 //-----------------------------------------------------------------------------
-bool MusicPlib::load(const char* filename)
+bool MusicPlib::load(const std::string& filename)
 {
     m_filename= loader->getPath(filename);
     return true;

src/sound_plib.hpp

@@ -47,7 +47,7 @@ public:
 
     virtual void update();
 
-    virtual bool load(const char* filename);
+    virtual bool load(const std::string &filename);
 
     virtual bool playMusic();
     virtual bool stopMusic();