Fix #818
Fix #819

Use 'opam update -u' to chain 'opam update' and 'opam upgrade --yes'
(Partially) update CHANGES
Fix #821

Use light blue instead of blue to see somthing on dark background
Fix #781 and #808

As we are not caching/building the +opam.tar.gz anymore, the checksum checking code was not used anymore. Fix that, and use a cache of upstream packages as well.
Merge branch 'master' of github.com:OCamlPro/opam

Conflicts:
	src/client/opamArg.ml
Merge pull request #831 from samoht/master

Various fixes