Fix memleak in setup

[Charles Wilson]

Charles Wilson wrote:
> If compress::decompress returns NULL, we need to clean up the allocated 
> specialized compress_* objects -- but NOT delete the passed-in 
> io_stream*.  The problem occurs Installer::installOne, but is corrected 
> by modifying the behavior of compress::decompress and the various 
> specialized decompression classes.
> 

Any objections if I check this in?

--
Chuck