Partial port of r59682 from py3k.

On Windows, when import fails to load a dll module, the message says
"error code 193" instead of a more informative text.

It turns out that FormatMessage needs additional parameters for some error codes.
For example: 193 means "%1 is not a valid Win32 application".
Since it is impossible to know which parameter to pass, we use
FORMAT_MESSAGE_IGNORE_INSERTS to get the raw message, which is still better
than the number.
diff --git a/Python/dynload_win.c b/Python/dynload_win.c
index fc641b9..98ebccb 100644
--- a/Python/dynload_win.c
+++ b/Python/dynload_win.c
@@ -194,7 +194,8 @@
 			errorCode = GetLastError();
 
 			theLength = FormatMessage(
-				FORMAT_MESSAGE_FROM_SYSTEM, /* flags */
+				FORMAT_MESSAGE_FROM_SYSTEM |
+				FORMAT_MESSAGE_IGNORE_INSERTS, /* flags */
 				NULL, /* message source */
 				errorCode, /* the message (error) ID */
 				0, /* default language environment */