Fix building with wxWidgets 2.8

src/compiledata.cpp

 
 #include <errno.h>
 
-void CompileMbrola(const char *mbrola_file)
+void CompileMbrola(const wxChar *mbrola_file)
 {//=================
 	char *p;
 	FILE *f_in;

src/espeakedit.cpp

 extern void init_z();
 extern void CompilePhonemeData(void);
 extern void CompileSampleRate(void);
-extern void CompileMbrola(const char *mbrola_file = NULL);
+extern void CompileMbrola(const wxChar *mbrola_file = NULL);
 extern void CompileIntonation();
 extern void InitSpectrumDisplay();
 extern void InitProsodyDisplay();