check for camlp4 presence and version in configure

fixes issue #431
Do not remove the lock when it has not been locked
Merge branch 'issue/431' of git://github.com/oandrieu/opam
Update generated configure file
autoconf: More helpful error message to indicate how to possibly fix the camlp4 missing problem
remove caml4boot from the test, as its not used and sometimes (on Debian?) not installed.
regenerate autoconf from 1465af9f99edd0533416ca397e7a7885488b769a
Merge pull request #433 from avsm/master

autoconf fixes for 3.12.1
Expose Cudf.string_of_packages
Fix the solver when newer packages have bigger deps than old ones.
Update CHANGES
Merge branch 'master' of github.com:OCamlPro/opam
Remove unused variable
truncate `opam list' output w.r.t. the size of the current terminal

Terminal size is determined using the `tput' or `stty' external commands.
No truncation when stdout is not a terminal (ie redirected to a file).
Merge pull request #436 from oandrieu/truncate-terminal-output

truncate `opam list` output w.r.t. the size of the current terminal
Fix embarrasing #439
Fix typo
Remove duplicated message about cached metadata on 'opam init'.
Speed-up 'opam update'.
Add a better error message in case of cyclic dependencies.

This should help debugging issues like #438