Fixed a bunch of compiler warnings.

diff --git a/windows/msgbox.c b/windows/msgbox.c
index 0b74905..a045d23 100644
--- a/windows/msgbox.c
+++ b/windows/msgbox.c
@@ -316,9 +316,9 @@
 
     memcpy(&msgboxa,msgbox,sizeof(msgboxa));
     if (msgbox->lpszCaption)	
-      lstrcpyWtoA(msgboxa.lpszCaption,msgbox->lpszCaption);
+      lstrcpyWtoA((LPSTR)msgboxa.lpszCaption,msgbox->lpszCaption);
     if (msgbox->lpszText)	
-      lstrcpyWtoA(msgboxa.lpszText,msgbox->lpszText);
+      lstrcpyWtoA((LPSTR)msgboxa.lpszText,msgbox->lpszText);
 
     return MessageBoxIndirect32A(&msgboxa);
 }