Add some logic to better support bash shells

Fix #533
Improve the performance of accessing the prefix file. This helps for non-standard repository hierarchy.
Rename shell/opam_install.sh
Remove install.sh which is not necessary anymore
Add a small script to easily build binary versions of OPAM
Improve the output of make_opam_binary.sh

Now:

    cp `sh make_opam_binary.sh 1.0.0` foo

works
Fix typo
Bump trunk version to 1.0.1
Fix 'opam switch foo' to correctly update the ~/.opam/opam-init/variable.{sh,zsh}

This was a regression introduced in 27b2f81deb0213e12e1aa1cf833b4d991a8653f6 (post 1.0.0)
jenkins: updates
Fix embarassing #551

This is a regression introduced in a7ec825f8dbc3c7a3fcb7a91617c0d623105125e (pre 1.0.0)
Update CHANGES
Add a regression test for #551
Merge pull request #550 from avsm/master

jenkins updates for liquidsoap
Display os & opam-version on internal errors as well
Update CHANGES
Merge branch 'master' of github.com:OCamlPro/opam
jenkins: update for riakc
Ignore OPAMSWITCH when displaying environment varilables (eg. on 'opam config env' or 'opam switch foo').

This fixes a regression introduced by 27b2f81deb0213e12e1aa1cf833b4d991a8653f6 where you cannot switch anymore when you have OPAMSWITCH set.
Merge branch 'master' of github.com:OCamlPro/opam