title: mysql2 gem installation failes on CentOS 6.4 x64 with MySQL 5.6
body: <p>Trying to install mysql2 gem on CentOS 6.4 x64 with MySQL 5.6 installed with rpm.</p>
  
  <p>Getting this:</p>
  
  <pre><code>    Installing mysql2 (0.3.11)
      Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
  
              /usr/local/rbenv/versions/1.9.3-p448/bin/ruby extconf.rb
      checking for rb_thread_blocking_region()... yes
      checking for rb_wait_for_single_fd()... yes
      checking for mysql.h... yes
      checking for errmsg.h... yes
      checking for mysqld_error.h... yes
      creating Makefile
  
      make
      compiling mysql2_ext.c
      compiling result.c
      compiling client.c
      client.c: In function Б─≤rb_raise_mysql2_errorБ─≥:
      client.c:98: warning: ISO C90 forbids mixed declarations and code
      client.c: In function Б─≤rb_mysql_client_socketБ─≥:
      client.c:590: warning: ISO C90 forbids mixed declarations and code
      linking shared-object mysql2/mysql2.so
      /usr/bin/ld: cannot find -lmysqlclient_r
      collect2: ld returned 1 exit status
      make: *** [mysql2.so] Error 1
  
  
      Gem files will remain installed in /usr/local/rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/mysql2-0.3.11 for inspection.
      Results logged to /usr/local/rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/mysql2-0.3.11/ext/mysql2/gem_make.out
  
      An error occurred while installing mysql2 (0.3.11), and Bundler cannot continue.
      Make sure that `gem install mysql2 -v '0.3.11'` succeeds before bundling.
  </code></pre>
  
  <p><strong>EDIT:</strong></p>
  
  <p>response from ldconfig -p | grep mysql</p>
  
  <pre><code>    libmysqlclient_r.so.16 (libc6,x86-64) =&gt; /usr/lib64/libmysqlclient_r.so.16
      libmysqlclient_r.so.15 (libc6,x86-64) =&gt; /usr/lib64/libmysqlclient_r.so.15
      libmysqlclient_r.so.14 (libc6,x86-64) =&gt; /usr/lib64/libmysqlclient_r.so.14
      libmysqlclient_r.so.12 (libc6,x86-64) =&gt; /usr/lib64/libmysqlclient_r.so.12
      libmysqlclient.so.16 (libc6,x86-64) =&gt; /usr/lib64/libmysqlclient.so.16
      libmysqlclient.so.15 (libc6,x86-64) =&gt; /usr/lib64/libmysqlclient.so.15
      libmysqlclient.so.14 (libc6,x86-64) =&gt; /usr/lib64/libmysqlclient.so.14
      libmysqlclient.so.12 (libc6,x86-64) =&gt; /usr/lib64/libmysqlclient.so.12
  </code></pre>