title: gem install mongrel fails with ruby 1.9.1
body: <p>I initiated myself into rails development yesterday.<br>
  I installed ruby 1.9.1, rubygems and rails.<br>
  Running <code>gem install mongrel</code> worked fine and ostensibly installed mongrel too. I am slightly puzzled because:</p>
  
  <ul>
  <li>script/server starts webrick by default</li>
  <li><code>which mongrel</code> returns nothing</li>
  <li><code>locate mongrel</code> returns lots of entries like</li>
  </ul>
  
  <pre>
  /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/mongrel-1.0.1
  /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/mongrel-1.0.1/lib
  /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/mongrel-1.0.1/lib/mongrel
  .
  .
  .
  /usr/local/bin/mongrel_rails
  /usr/local/lib/ruby/gems/1.9.1/cache/mongrel-1.1.5.gem
  /usr/local/lib/ruby/gems/1.9.1/doc/actionpack-2.3.2/rdoc/files/lib/action_controller/vendor/rack-1_0/rack/handler/evented_mongrel_rb.html
  /usr/local/lib/ruby/gems/1.9.1/doc/actionpack-2.3.2/rdoc/files/lib/action_controller/vendor/rack-1_0/rack/handler/mongrel_rb.html
  /usr/local/lib/ruby/gems/1.9.1/doc/actionpack-2.3.2/rdoc/files/lib/action_controller/vendor/rack-1_0/rack/handler/swiftiplied_mongrel_rb.html
  /usr/local/lib/ruby/gems/1.9.1/gems/actionpack-2.3.2/lib/action_controller/vendor/rack-1.0/rack/handler/evented_mongrel.rb
  /usr/local/lib/ruby/gems/1.9.1/gems/actionpack-2.3.2/lib/action_controller/vendor/rack-1.0/rack/handler/mongrel.rb
  /usr/local/lib/ruby/gems/1.9.1/gems/actionpack-2.3.2/lib/action_controller/vendor/rack-1.0/rack/handler/swiftiplied_mongrel.rb
  /usr/local/lib/ruby/gems/1.9.1/gems/mongrel-1.1.5
  .
  .
  .
  </pre>
  
  <p>Does look like I have mongrel installed (both the default installation and my custom install). So why doesn't which mongrel return something.</p>
  
  <p>Also trying to reinstall mongrel using <code>gem install mongrel</code> returns throws its own set of exceptions:</p>
  
  <pre>
  Building native extensions.  This could take a while...
  ERROR:  Error installing mongrel:
      ERROR: Failed to build gem native extension.
  
  /usr/local/bin/ruby extconf.rb install mongrel
  checking for main() in -lc... yes
  creating Makefile
  
  make
  gcc -I. -I/usr/local/include/ruby-1.9.1/i386-darwin9.7.0 -I/usr/local/include/ruby-1.9.1/ruby/backward -I/usr/local/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -D_XOPEN_SOURCE=1 -O2 -g -Wall -Wno-parentheses  -fno-common -pipe -fno-common  -o http11.o -c http11.c
  http11.c: In function 'http_field':
  http11.c:77: error: 'struct RString' has no member named 'ptr'
  http11.c:77: error: 'struct RString' has no member named 'len'
  http11.c:77: warning: left-hand operand of comma expression has no effect
  http11.c:77: warning: statement with no effect
  http11.c: In function 'header_done':
  http11.c:172: error: 'struct RString' has no member named 'ptr'
  http11.c:174: error: 'struct RString' has no member named 'ptr'
  http11.c:176: error: 'struct RString' has no member named 'ptr'
  http11.c:177: error: 'struct RString' has no member named 'len'
  http11.c: In function 'HttpParser_execute':
  http11.c:298: error: 'struct RString' has no member named 'ptr'
  http11.c:299: error: 'struct RString' has no member named 'len'
  make: *** [http11.o] Error 1
  </pre>