Fix typo in config/os/mingw32/error_constants.h

[Gerald Pfeifer]

By chance I noticed the following typo and went ahead and installed
the patch below as obvious.

Gerald

2007-12-29  Gerald Pfeifer  <gerald@pfeifer.com>

	* config/os/mingw32/error_constants.h: Fix typo in comment.

Index: config/os/mingw32/error_constants.h
===================================================================
--- config/os/mingw32/error_constants.h	(revision 131218)
+++ config/os/mingw32/error_constants.h	(working copy)
@@ -43,7 +43,7 @@
 
 namespace posix_error {
 // Most of the commented-out error codes are socket-related and could be
-// replaced bu Winsock WSA-prefixed equivalents.
+// replaced by Winsock WSA-prefixed equivalents.
   enum posix_errno
     {
 //    address_family_not_supported = 		EAFNOSUPPORT,