Attempt to simplify and sanitize git handling
Merge pull request #1640 from OCamlPro/git-fix

Attempt to simplify and sanitize git handling
switch import: import roots even if already installed
Merge pull request #1652 from OCamlPro/fix-import-roots

switch import: import roots even if already installed
Merge pull request #1655 from samoht/search-files

`opam search` now look in configurable locations.
Improve 'Already up-to-date' when some packages aren't at their latest version

ref: #1645 (first point)
Rename src/scripts src/tools
Move some general use functions from OpamState to OpamGlobals
Fixed color handling wrt env vars
Two more functions in OpamFile's API
Fixed the 'make fast' target
Remove duplicate Downloading messages
Merge pull request #1654 from OCamlPro/up-to-date

Improve 'Already up-to-date' when some packages aren't at their latest version
Merge pull request #1653 from OCamlPro/some-reorg

Some internal reorganisation, small cleanup and fixes
Improve the API exposed by opam_admin_top