title: cannot load such file -- zlib even after using rvm pkg install zlib
body: <p>I installed zlib package and ruby 1.9.3 using rvm, but whenever I try to install
  gems it says
  <code>cannot load such file -- zlib</code></p>
  
  <p>The commands I used to install are</p>
  
  <pre><code>$ rvm install 1.9.3
  </code></pre>
  
  <pre>
  $ rvm pkg install zlib
  
  $ rvm reinstall 1.9.3 --with-readline-dir=/home/username/.rvm/usr \
      --with-iconv-dir=/home/username/.rvm/usr \
      --with-zlib-dir=/home/username/.rvm/usr \
      --with-openssl-dir=/home/username/.rvm/usr
  
  $ rvm use 1.9.3
  
  $ gem install heroku
  ERROR: Loading command: install (LoadError)
      cannot load such file -- zlib
  ERROR: While executing gem ... (NameError)
      uninitialized constant Gem::Commands::InstallCommand
  </pre>
  
  <p>All the help on this subject tells me to just do <code>rvm pkg install zlib</code>, and
  then reinstall the ruby with <code>--with-zlib-dir=/home/username/.rvm/usr</code>, but this
  didn't work.</p>