insighttoolkit4 on i386 (+sse2)

[Gert Wollny <gw.fossdev@gmail.com>]

Dear all, 

since every time upstream release a new major version, tests are
failing on i386 - a result from using the i387 FPU instructions, and
since I only know this after about 8 hours of build time, I have now
decided that with the latest release (4.12) I'd enable sse2.

Incidentally, I also don't think it makes much sense to support pre-
Pentium4 hardware with ITK, but if someone thinks otherwise, you are
cordially invited to co-maintain the package :)

Best, 
Gert