Win32GUI: Gather raw_print text and display it all in single dialog

Defined strbuf_t and related routines to support dynamically sized
strings. Modified strip_newline() to strip the last newline in a string
instead of the first.

Simplified splash window code using new strbuf_t.

Prior to exiting game, re-enable getreturn and call wait_synch() in
case there is buffered raw prints that must be displayed to user.

include/hack.h

@@ -151,6 +151,12 @@ enum game_end_types {
     ASCENDED
 };
 
+typedef struct strbuf {
+    int    len;
+    char * str;
+    char   buf[256];
+} strbuf_t;
+
 #include "align.h"
 #include "dungeon.h"
 #include "monsym.h"