add an extra option into the command install, and allow to mount extended partitions.

stage2/shared.h

@@ -695,6 +695,7 @@ char *convert_to_ascii (char *buf, int c, ...);
 int get_cmdline (char *prompt, char *cmdline, int maxlen,
 		 int echo_char, int history);
 int substring (char *s1, char *s2);
+char *nul_terminate (char *str);
 int get_based_digit (int c, int base);
 int safe_parse_maxint (char **str_ptr, int *myint_ptr);
 int memcheck (int start, int len);