Merge pull request #1195 from OCamlPro/small-UI-fixes

small display and command-line fixes
Merge pull request #1197 from OCamlPro/fix-unneeded-download

Skip unneeded package downloads
Changed default preferences to avoid downgrades when possible.
Added help entry for OPAMCRITERIA with default value printed out.
Reorganised dose patches to match the ones now present in dose 3.1.2 opam package
Experimenting a different default value for the external solver preferences
Restored pointer to real upstream sources of ocamlgraph in src_ext
Moved version to 1.8.4, that includes the graphml output moved there from dose
Step up ocamlgraph to 1.8.3
Merge pull request #1201 from rdicosmo/fix-ext-src

Fix ocamlgraph in src_ext
Merge pull request #1200 from rdicosmo/new-solver-criteria

Streamline external solver criteria
Debug solver conflicts
Fixed a bug with upstream-removed packages that could skip an uninstall

and then fail to install with a 'multiple versions' error
Accept to (re)install upstream-removed packages if their metadata is still present

the previous check was too strict and made opam-rt fail
Fixed cleanup of metadata