title: Can't run the command -- rake:install
body: <p>When I run the command <code>rake:install</code>, I get this error message:</p>
  
  <pre><code>WARNING: 'require 'rake/rdoctask'' is deprecated.  Please use 'require 'rdoc/task' (in RDoc 2.4.2+)' instead.
      at /Users/adam/.rvm/gems/ruby-1.9.2-p290/gems/rake-0.9.2.2/lib/rake/rdoctask.rb
    Successfully built RubyGem
    Name: mysql2psql
    Version: 0.1.0
    File: mysql2psql-0.1.0.gem
  Executing "ruby -S gem install ./pkg/mysql2psql-0.1.0.gem":
  ruby -S gem install ./pkg/mysql2psql-0.1.0.gem
  Building native extensions.  This could take a while...
  ERROR:  Error installing ./pkg/mysql2psql-0.1.0.gem:
      ERROR: Failed to build gem native extension.
  
          /Users/adam/.rvm/rubies/ruby-1.9.2-p290/bin/ruby extconf.rb
  checking for pg_config... no
  
    ===========   WARNING   ===========
  
    You are building this extension on OS X without setting the 
    ARCHFLAGS environment variable, and pg_config wasn't found in 
    your PATH. If you are seeing this message, that means that the 
    build will probably fail.
  
    If it does, you can correct this by either including the path 
    to 'pg_config' in your PATH or setting the environment variable 
    ARCHFLAGS to '-arch &lt;arch&gt;' before building.
  
    For example:
    (in bash) $ export PATH=/opt/local/lib/postgresql84/bin:$PATH                  
              $ export ARCHFLAGS='-arch x86_64'
    (in tcsh) % set path = ( /opt/local/lib/postgresql84/bin $PATH )
              % setenv ARCHFLAGS '-arch x86_64'
  
    Then try building again.
  
    ===================================
  
  MacOS X build: fixing architecture flags:
  checking for libpq-fe.h... no
  Can't find the 'libpq-fe.h header
  *** 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=/Users/radek/.rvm/rubies/ruby-1.9.2-p290/bin/ruby
      --with-pg
      --without-pg
      --with-pg-config
      --without-pg-config
      --with-pg-dir
      --without-pg-dir
      --with-pg-include
      --without-pg-include=${pg-dir}/include
      --with-pg-lib
      --without-pg-lib=${pg-dir}/lib
      --enable-static-build
      --disable-static-build
  
  
  Gem files will remain installed in /Users/adam/.rvm/gems/ruby-1.9.2-p290/gems/pg-0.9.0 for inspection.
  Results logged to /Users/adam/.rvm/gems/ruby-1.9.2-p290/gems/pg-0.9.0/ext/gem_make.out
  rake aborted!
  Command failed with status (1): [ruby -S gem install ./pkg/mysql2psql-0.1.0...]
  
  Tasks: TOP =&gt; install
  (See full trace by running task with --trace)
  </code></pre>
  
  <p>Apparently is the problem in the <code>pg</code> gem, but when I check the list of installed gems in my application, so there is <code>* pg (0.13.2)</code></p>
  
  <p>So what I am missing yet?</p>