fusion: use HeapAlloc, not strdup, to avoid malloc/HeapFree mismatch [take 2]

[Dan Kegel]

Can't mix strdup and HeapFree.

Fixes first two Valgrind errors in
http://kegel.com/wine/valgrind/logs-2008-05-25/vg-fusion_asmcache.txt

[The part James objected to will follow in a second patch.  He's happy
with both now.]
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