title: Cannot bundle update & install in a redmine migration
body: <p>I migrated to Debian 9 a Redmine application v 2.5.0. After copying all files, it is impossible to bundle update or install.</p>
  
  <p>I have installed <code>default-libmysqlclient-dev</code> and then <code>gem install mysql</code> 
  but without success.</p>
  
  <p>Bundle update give this output:</p>
  
  <pre><code>Your Gemfile lists the gem activerecord-jdbcmysql-adapter (&gt;= 0) more than     once.
  You should probably keep only one of them.
  While it's not a problem now, it could cause errors if you change the     version of one of them later.
  Fetching gem metadata from https://rubygems.org/..............
  Fetching version metadata from https://rubygems.org/...
  Fetching dependency metadata from https://rubygems.org/..
  Resolving dependencies...
  Using rake 12.3.2 (was 10.1.1)
  Using concurrent-ruby 1.1.5
  Using multi_json 1.13.1 (was 1.9.2)
  Using builder 3.0.0
  Using erubis 2.7.0
  Using journey 1.0.4
  Using rack 1.4.7 (was 1.4.5)
  Using hike 1.2.3
  Using tilt 1.4.1
  Using mime-types 1.25.1
  Using polyglot 0.3.5 (was 0.3.4)
  Using arel 3.0.3
  Using tzinfo 0.3.55 (was 0.3.39)
  Using bundler 1.13.6
  Using mini_portile2 2.4.0
  Using ffi 1.10.0
  Using coderay 1.1.2 (was 1.1.0)
  Using json 1.8.6 (was 1.8.1)
  Using thor 0.20.3 (was 0.18.1)
  Using metaclass 0.0.4
  Installing mysql 2.8.1 with native extensions
  Using mysql2 0.3.21 (was 0.3.15)
  Using net-ldap 0.3.1
  Installing pg 1.1.4 (was 0.17.1) with native extensions
  Using ruby-openid 2.3.0
  Using redcarpet 2.3.0
  Using rmagick 3.0.0 (was 2.13.2)
  Using rubyzip 1.2.2
  Using shoulda-context 1.0.2
  Installing sqlite3 1.4.0 (was 1.3.9) with native extensions
  Using yard 0.9.18 (was 0.8.7.3)
  Using i18n 0.9.5 (was 0.6.9)
  Using rack-cache 1.9.0 (was 1.2)
  Using rack-test 0.6.3 (was 0.6.2)
  Using rack-ssl 1.3.4 (was 1.3.3)
  Using sprockets 2.2.3 (was 2.2.2)
  Using treetop 1.4.15
  Using nokogiri 1.10.2
  Using childprocess 0.9.0
  Using rdoc 3.12.2
  Using mocha 1.8.0 (was 1.0.0)
  Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
  
      current directory: /var/lib/gems/2.3.0/gems/mysql-2.8.1/ext/mysql_api
  /usr/bin/ruby2.3 -r ./siteconf20190326-30772-4a7i24.rb extconf.rb
  checking for mysql_ssl_set()... yes
  checking for rb_str_set_len()... yes
  checking for rb_thread_start_timer()... no
  checking for mysql.h... yes
  *** extconf.rb failed ***
  Could not create Makefile due to some reason, probably lack of necessary
  libraries and/or headers.  Check the mkmf.log file for more details.  You may
  need configuration options.
  
  Provided configuration options:
      --with-opt-dir
      --without-opt-dir
      --with-opt-include
      --without-opt-include=${opt-dir}/include
      --with-opt-lib
      --without-opt-lib=${opt-dir}/lib
      --with-make-prog
      --without-make-prog
      --srcdir=.
      --curdir
      --ruby=/usr/bin/$(RUBY_BASE_NAME)2.3
      --with-mysql-config
      --without-mysql-config
  extconf.rb:67:in `&lt;main&gt;': uninitialized constant Config (NameError)
  Did you mean?  RbConfig
                 CONFIG
  
  To see why this extension failed to compile, please check the mkmf.log which can be found here:
  
    /var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/mysql-2.8.1/mkmf.log
  
  extconf failed, exit code 1
  
  Gem files will remain installed in /var/lib/gems/2.3.0/gems/mysql-2.8.1 for inspection.
  Results logged to /var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/mysql-    2.8.1/gem_make.out
  
  An error occurred while installing mysql (2.8.1), and Bundler cannot continue.
  Make sure that `gem install mysql -v '2.8.1'` succeeds before bundling.
  </code></pre>
  
  <p>When I try to install bundle, I have the same error as bellow: </p>
  
  <pre><code>An error occurred while installing json (1.8.1), and Bundler cannot continue.
  Make sure that `gem install json -v '1.8.1'` succeeds before bundling.
  </code></pre>