added const to the prompt char * in the proto

lib/getpass.h

@@ -29,7 +29,7 @@
 /*
  * Returning NULL will abort the continued operation!
  */
-char* getpass_r(char *prompt, char* buffer, size_t buflen );
+char* getpass_r(const char *prompt, char* buffer, size_t buflen );
 #endif
 
 #endif