[krbdev.mit.edu #7391] installer reuses guids for 32- and 64-bit paths

[Benjamin Kaduk via RT]

There are still a few GUIDs hardcoded in files.wxi; some of them are for components that install 
differently on 32- and 64-bit systems.  This is outside the spec and should be corrected by 
having separate guids for the different versions and using variable expansion as is done for 
most of the components in that file.  Registry keys in particular are affected.