yum-presto not on by default

[Muayyad AlSadi]

setting xz level to 2 seems reasonable

but how about thinking about a better solution:

Q: what put the gpg signatures ?
A: rpmbuild (or something that call it like mock)

so how about to make rpmbuild generate gpg and checksums on both
uncompressed and uncompressed payloads

so every rpm would carry the signatures and checksums if its payload
is decompressed beside the typical  signatures and checksums

maybe this is not for F12 as it could require some changes in rpm,
yum, deltarpm, ...etc.

but this is the right thing
> http://fedoratux.blogspot.com/2009/05/xz-compression.html
the default is -6
we are talking about -2
could you please do your benchmarks at that level please