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I modified the patch some.  Removed include <fcntl.h> since
that didn't seem necessary.  Changed the #ifdef slightly. 
Modified comments.

I now understand that anonymous memory was allowed on Unix
before (in 2.3 and pre 2.4.2).  I backported the non-feature
enhancements of this patch (not dup()ing -1).  So 2.4.3
should work like 2.4.1 and earlier.  It would be great if
you can test out 2.5 and 2.4.3 from SVN.

Committed revision 42244.
Committed revision 42245. (2.4)