Win32: additional error code NGX_EEXIST_FILE (ticket #910).

On Windows there are two possible error codes which correspond to
the EEXIST error code: ERROR_FILE_EXISTS used by CreateFile(CREATE_NEW),
and ERROR_ALREADY_EXISTS used by CreateDirectory().

MoveFile() seems to use both: ERROR_ALREADY_EXISTS when moving within
one filesystem, and ERROR_FILE_EXISTS when copying a file to a different
drive.

src/os/unix/ngx_errno.h

@@ -25,6 +25,7 @@ typedef int               ngx_err_t;
 #define NGX_EACCES        EACCES
 #define NGX_EBUSY         EBUSY
 #define NGX_EEXIST        EEXIST
+#define NGX_EEXIST_FILE   EEXIST
 #define NGX_EXDEV         EXDEV
 #define NGX_ENOTDIR       ENOTDIR
 #define NGX_EISDIR        EISDIR

src/os/win32/ngx_errno.h

@@ -25,8 +25,14 @@ typedef DWORD                      ngx_err_t;
 #define NGX_ENOPATH                ERROR_PATH_NOT_FOUND
 #define NGX_ENOMEM                 ERROR_NOT_ENOUGH_MEMORY
 #define NGX_EACCES                 ERROR_ACCESS_DENIED
-/* it's seems that ERROR_FILE_EXISTS is not appropriate error code */
+/*
+ * there are two EEXIST error codes:
+ * ERROR_FILE_EXISTS used by CreateFile(CREATE_NEW),
+ * and ERROR_ALREADY_EXISTS used by CreateDirectory();
+ * MoveFile() uses both
+ */
 #define NGX_EEXIST                 ERROR_ALREADY_EXISTS
+#define NGX_EEXIST_FILE            ERROR_FILE_EXISTS
 /*
  * could not found cross volume directory move error code,
  * so use ERROR_WRONG_DISK as stub one