Merge pull request #392 from avsm/master

improve help text
Bump trunk version to 0.9.2
Merge branch 'master' of github.com:OCamlPro/opam
Fix 'opam-mk-repo -a'
Look for opam-lib to check if OPAM is up-to-date and do no ask the user if he really wants to continue as it's a bit annoying.
Update CHANGES
Do not remove log file of a command with an error.
Fix 'opam-mk-repo --index'
Update CHANGES
Remove left-over pinned cache (this can happen sometimes when the pinned package failed to build).
Update CHANGES
Be a bit less aggressive when caching the cache of pinned package.
Fix previous commit ... this should work now.
Be more robust when an installed package disapear.
Fix 'opam help' to display the main help page.

This should fix #397 (thx to @dbuenzli)
Fix typo
Update generated man pages
Update API docs
'opam update <pinned-package>' works.

This should fix #396 (which is quite annoying when you don't have network access)
Update CHANGES