Fix pretty-printing of OPAM files

Continue #998
Merge pull request #999 from samoht/master

Fix pretty-printing of OPAM files
Drop the leading '/' from the prefix
Merge pull request #1003 from dsheets/relative-prefix

Drop the leading '/' from the prefix
Removing warning messages when uninstalling a package which failed to install
Closes #1002
Ignore emacs lock files when rsync'ing a local repo (#983)
Merge pull request #1010 from AltGr/refs/heads/two-small-fixes

Fix #983, #1002
List the offending fields

Fix #1016
Update CHANGES
Merge pull request #1017 from samoht/master

List offending fields
Fixed messages concerning versions of pinned packages
(I was getting: `The dependency ocaml<=pinned of package js_of_ocaml.1.3.2 is not available because the package has been pinned.`)
Fixes #1024
Merge pull request #1025 from AltGr/fix-pinned-message

Fixed messages concerning versions of pinned packages
Added a new 'opam-installer' script to make .install files usable outside of opam
Fixed opam-admin stats for packages in sub-dirs
Closes #1023
Merge pull request #1026 from AltGr/opam-installer

Added a new 'opam-installer' script to make .install files usable outside of opam
Merge pull request #1028 from AltGr/fix-stats

Fixed opam-admin stats for packages in sub-dirs
opam-admin: add a '--resolve' option that builds just the archives you need for a specific installation
Merge pull request #1031 from AltGr/opam-admin-resolve

opam-admin: added '--resolve'
Defined empty_universe

This may enable users of opam_lib not to break if we add fields
Merge pull request #1033 from AltGr/empty-universe

Defined empty_universe