fix parallel build of documentation
import: implement generic retry mechanism
define Autobuild.warn and Autobuild.error the same way than in autoproj
fix empty lines popping up in the output
use the message / warn API instead of STDERR/STDOUT
remove debugging outputs
release 1.6.2.b1
fix usage of Autoproj.message instead of Autobuild.message in warn and error
fix spurious empty lines appearing in autobuild output
fix unsynchronized manipulation of display structures in #message, #progress* and friends
fix recursive locking in progress_start
remove the display of "updating %package" when retrying
try to cleanup puts vs. print logic in message API
require 'thread' as it is needed to get Mutex on Ruby 1.8
implement Autobuild.silent? and .silent= to silence all messages from autobuild
define env_source_before and env_source_after to replace env_source_file

env_source_file is still defined and calls env_source_file for backward
compatibility reasons.
fix #repository_id for the git importer

The goal of #repository_id is to tell the caller whether two importers
can work on the same working copy or not. In the case of git, this
is possible as soon as the repo is the same (the branch does not matter)
fix export_env_sh calling env_source_* instead of accessing the attributes
subcommand: properly handle an Interrupt exception that would be raised in the child process
define Autobuild.silent { }