Removed inclusion of wine/winestring.h from winbase.h and added it to
the C files that need it.

diff --git a/dlls/kernel/format_msg.c b/dlls/kernel/format_msg.c
index eab7922..316f78a 100644
--- a/dlls/kernel/format_msg.c
+++ b/dlls/kernel/format_msg.c
@@ -14,6 +14,7 @@
 #include "winerror.h"
 #include "winnls.h"
 #include "wine/unicode.h"
+#include "wine/winestring.h"
 
 #include "heap.h"
 #include "debugtools.h"