COMP: Fix missing itkdouble-conversion library when using packaged Slicer

Update ITKv4 version to include ITK commit f228cd4

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COMP: The install path for DoubleConversion lib was wrong.

As reported by Vladimir Chalupecky, the install path for
double-conversion libraries was wrong. I fixed and tested
that, and used the ITK Module-generated path variables
instead of ad hoc variables local to the DoubleConversion
Module.

See https://github.com/Kitware/ITK/commit/f228cd4
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Thanks to Marianna Jakab for reporting the issue.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21858 3bd1e089-480b-0410-8dfb-8563597acbee