using prefixes via their extended command names

Trying to use #reqmenu/#rush/#run/#fight prefixes by their extended
command names didn't work because rhack()'s post-processing was stuck
dealing with the entry for the '#' key after using doextcmd() to run
any command.  Use a static variable (actually a global one since I put
it into struct g) to notify rhack() of the command that ultimately got
executed.

src/decl.c

@@ -231,6 +231,7 @@ const struct instance_globals g_init = {
     WIN_ERR, /* en_win */
     FALSE, /* en_via_menu */
     UNDEFINED_VALUE, /* last_command_count */
+    NULL, /* ext_tlist */
 
     /* dbridge.c */
     UNDEFINED_VALUES, /* occupants */