title: can't install postgres ruby gem
body: <p>I am having trouble install postgres on OSX mavericks. I have tried to follow the numerous guides on Stackoverflow with no luck. I installed the postgres.app and also postgres. I have found my pg_config file and tried this command: </p>
  
  <pre><code>gem install pg -- --with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config
  </code></pre>
  
  <p>But I am still getting this error</p>
  
  <pre><code>Building native extensions with: '--with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config .'
  This could take a while...
  ERROR:  Error installing pg:
  ERROR: Failed to build gem native extension.
  
  /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb --with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config .
  Using config values from /Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config
  checking for libpq-fe.h... yes
  checking for libpq/libpq-fs.h... yes
  checking for pg_config_manual.h... yes
  checking for PQconnectdb() in -lpq... no
  checking for PQconnectdb() in -llibpq... no
  checking for PQconnectdb() in -lms/libpq... no
  Can't find the PostgreSQL client library (libpq)
  *** 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=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
  --with-pg
  --without-pg
  --with-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}/
  --with-pqlib
  --without-pqlib
  --with-libpqlib
  --without-libpqlib
  --with-ms/libpqlib
  --without-ms/libpqlib
  
  extconf failed, exit code 1
  
  Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/pg-0.17.1 for inspection.
  Results logged to /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-13/2.0.0/pg-0.17.1/gem_make.out
  </code></pre>