Various changes to FDC emulation.

Support for multiple disc image formats.
Added preliminary FDI support.

src/config.h

@@ -6,6 +6,7 @@ void config_set_string(char *head, char *name, char *val);
 char *get_filename(char *s);
 void append_filename(char *dest, char *s1, char *s2, int size);
 void put_backslash(char *s);
+char *get_extension(char *s);
 
 void config_load(char *fn);
 void config_save(char *fn);