Merge pull request #898 from samoht/master

Fix #858
Merge pull request #899 from samoht/885

885
New option 'install --deps-only'
Closes #889
Fix: broken upgrade with complex cases of removed packages
Merge pull request #900 from AltGr/install-deps-only

New option 'install --deps-only'
Merge pull request #901 from AltGr/fix-complex-upgrade

Fix: broken upgrade with complex cases of removed packages
Workaround failure of aspcud when only downgrade is possible
Merge pull request #902 from AltGr/fix-aspcud

Workaround failure of aspcud when only downgrade is possible [WIP]
Turning some warnings into 'notes'
Closes #890 -- thanks for the idea
Merge pull request #907 from AltGr/DONT-PANIC-THIS-IS-JUST-A-NOTE

Turning some warnings into 'notes'
External solver failure: better messages, and logging cudf file
Added a --no-aspcud option to disable the external solver
Merge pull request #908 from AltGr/aspcud-fail-log-cudf

External solver failure: better messages, and logging cudf file
Merge branch 'master' of github.com:OCamlPro/opam into compat-mode

Conflicts:
	src/client/opamArg.ml
	src/core/opamGlobals.ml