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.

sys/share/pcsys.c

@@ -546,6 +546,8 @@ msexit()
         getreturn("to end");
     synch_cursor();
 #endif
+    getreturn_enabled = TRUE;
+    wait_synch();
     return;
 }
 #endif /* MICRO || WIN32 || OS2 */