title: Date-performance installation error
body: <p>When I try install the gem <a href="https://github.com/rtomayko/date-performance" rel="nofollow">date-performance</a> with command <code>gem install date-performance</code>, I get this error:</p>
  
  <pre><code>date_performance.c:16:14: erro: static declaration of ‘rb_cRational’ follows non-static declaration
  ...
  date_performance.c:365:3: aviso: ISO C90 forbids mixed declarations and code [-pedantic]
  make: ** [date_performance.o] Erro 1
  </code></pre>
  
  <p>How to fix it?</p>
  
  <p><strong>Udpate:</strong></p>
  
  <p>The SO is Ubuntu and I use ruby 1.9</p>
  
  <p>Follows the full error:</p>
  
  <pre><code>/home/vmlellis/.rvm/rubies/ruby-1.9.3-p392/bin/ruby extconf.rb
  creating Makefile
  
  make
  compiling date_performance.c
  date_performance.c:16:14: erro: static declaration of ‘rb_cRational’ follows non-static declaration
  In file included from /home/vmlellis/.rvm/rubies/ruby-1.9.3-p392/include/ruby-1.9.1/ruby.h:32:0,
                   from date_performance.c:9:
  /home/vmlellis/.rvm/rubies/ruby-1.9.3-p392/include/ruby-1.9.1/ruby/ruby.h:1271:19: nota: previous declaration of ‘rb_cRational’ was here
  date_performance.c: Na função ‘rb_date_new’:
  date_performance.c:200:5: aviso: ISO C90 forbids mixed declarations and code [-pedantic]
  date_performance.c:219:3: aviso: ISO C90 forbids mixed declarations and code [-pedantic]
  date_performance.c: Na função ‘rb_date_strftime’:
  date_performance.c:253:31: erro: ‘struct RString’ has no member named ‘ptr’
  date_performance.c:254:29: erro: ‘struct RArray’ has no member named ‘ptr’
  date_performance.c:268:30: erro: ‘struct RString’ has no member named ‘ptr’
  date_performance.c:269:17: erro: ‘struct RString’ has no member named ‘len’
  date_performance.c:277:30: erro: ‘struct RString’ has no member named ‘ptr’
  date_performance.c:279:5: aviso: implicit declaration of function ‘bzero’ [-Wimplicit-function-declaration]
  date_performance.c:279:5: aviso: incompatible implicit declaration of built-in function ‘bzero’ [habilitado por padrão]
  date_performance.c:284:23: erro: ‘struct RString’ has no member named ‘len’
  date_performance.c: Na função ‘rb_date_strptime’:
  date_performance.c:304:27: erro: ‘struct RString’ has no member named ‘ptr’
  date_performance.c:305:27: erro: ‘struct RString’ has no member named ‘ptr’
  date_performance.c:329:3: aviso: implicit declaration of function ‘strptime’ [-Wimplicit-function-declaration]
  date_performance.c: Na função ‘rb_date_compare’:
  date_performance.c:350:3: aviso: ISO C90 forbids mixed declarations and code [-pedantic]
  date_performance.c:353:5: aviso: comentários usando o estilo do C++ não são permitidos na ISO C90 [habilitado por padrão]
  date_performance.c:353:5: aviso: (isso será relatado apenas uma vez por aquivo de entrada) [habilitado por padrão]
  date_performance.c:365:3: aviso: ISO C90 forbids mixed declarations and code [-pedantic]
  make: ** [date_performance.o] Erro 1
  </code></pre>