#4973 Build fails on non-Windows OS

#4973 Build fails on non-Windows OS

Hi,
I don't have permission to re-open #4896 so I created a duplicate
#4973 and took the liberty of assigning the same priority and
milestone as #4896.
The changes included in r3445 cause the build to complete, but the
`prepend-header` target does not work correctly. I confirmed this by
building jquery-ui on Windows and on Ubuntu and comparing the content
of the `dist` directory (modulo line endings). Look at
`jquery.effects.*.min.js` for example.
I've attached a patch to #4973 that resolves the problem for me. The
patch has been tested on Windows 7 and Ubuntu 9.10.
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