Additional info trying a second round:

Setting up redmine (1.3.2+dfsg1-1ubuntu1) ...
dbconfig-common: writing config to /etc/dbconfig-common/redmine/instances/default.conf

Creating config file /etc/redmine/default/database.yml.new with new version
granting access to database redmine_default for redmine@localhost: already exists.
creating database redmine_default: already exists.
dbconfig-common: flushing administrative password
Populating database for redmine instance "default".
This may take a while.
NOTE: Gem.source_index is deprecated, use Specification. It will be removed on or after 2011-11-01.
Gem.source_index called from /usr/share/redmine/config/../vendor/rails/railties/lib/rails/gem_dependency.rb:21.
NOTE: Gem::SourceIndex#initialize is deprecated with no replacement. It will be removed on or after 2011-11-01.
Gem::SourceIndex#initialize called from /usr/share/redmine/config/../vendor/rails/railties/lib/rails/vendor_gem_source_index.rb:100.
NOTE: Gem::SourceIndex#add_spec is deprecated, use Specification.add_spec. It will be removed on or after 2011-11-01.
Gem::SourceIndex#add_spec called from /usr/lib/ruby/vendor_ruby/1.8/rubygems/source_index.rb:91.
NOTE: Gem::SourceIndex#add_spec is deprecated, use Specification.add_spec. It will be removed on or after 2011-11-01.
Gem::SourceIndex#add_spec called from /usr/lib/ruby/vendor_ruby/1.8/rubygems/source_index.rb:91.
NOTE: Gem::SourceIndex#add_spec is deprecated, use Specification.add_spec. It will be removed on or after 2011-11-01.
Gem::SourceIndex#add_spec called from /usr/lib/ruby/vendor_ruby/1.8/rubygems/source_index.rb:91.
NOTE: Gem::SourceIndex#add_spec is deprecated, use Specification.add_spec. It will be removed on or after 2011-11-01.
Gem::SourceIndex#add_spec called from /usr/lib/ruby/vendor_ruby/1.8/rubygems/source_index.rb:91.
NOTE: Gem::SourceIndex#add_spec is deprecated, use Specification.add_spec. It will be removed on or after 2011-11-01.
Gem::SourceIndex#add_spec called from /usr/lib/ruby/vendor_ruby/1.8/rubygems/source_index.rb:91.
NOTE: Gem::SourceIndex#add_spec is deprecated, use Specification.add_spec. It will be removed on or after 2011-11-01.
Gem::SourceIndex#add_spec called from /usr/lib/ruby/vendor_ruby/1.8/rubygems/source_index.rb:91.
NOTE: Gem::SourceIndex#add_spec is deprecated, use Specification.add_spec. It will be removed on or after 2011-11-01.
Gem::SourceIndex#add_spec called from /usr/lib/ruby/vendor_ruby/1.8/rubygems/source_index.rb:91.
!!! The bundled mysql.rb driver has been removed from Rails 2.2. Please install the mysql gem and try again: gem install mysql.
rake aborted!
libmysqlclient.so.16: cannot open shared object file: No such file or directory - /usr/local/lib/site_ruby/1.8/i686-linux/mysql.so

Tasks: TOP => db:migrate => environment
(See full trace by running task with --trace)
Error when running rake db:migrate, check database configuration.
/var/lib/dpkg/info/redmine.postinst: 279: exit: Illegal number: -1
dpkg: error processing redmine (--configure):
 subprocess installed post-installation script returned error exit status 2
Errors were encountered while processing:
 redmine

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Note

$ ls -l /usr/local/lib/site_ruby/1.8/i686-linux/mysql.so
-rwxrwxr-x 1 root staff 163033 Nov  1  2012 /usr/local/lib/site_ruby/1.8/i686-linux/mysql.so

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MySQL was reinstalled immediately before trying to install/configure redmine.
This is Ubuntu 12.04 LTS.

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Please do not hesitate asking for more informetion.  And thanks for the amazing work!