Adds VariantClear and removes unnecessary variant type assignment that may cause 
heap corruption.

This reverts commit b157969d.

Fixes a crash in native cryptui.dll when viewing certificate properties.

It means that the data is stored directly in pItem->byte_offs instead
of the byte offset pointed to by it.

This prevents some driver warnings when using language features from
1.20, like "first class arrays".

Just unsetting SFLAG_INTEXTURE doesn't work for FBOs because the
drawable and texture are the same there (and ModifyLocation() is the
correct way to do this anyway). Fixes another ddraw test failure with
FBO ORM.