gema instalar mongrel falla con ruby ​​1.9.1

Me inicié en el desarrollo de rieles ayer.
Instalé ruby ​​1.9.1, rubygems y rieles.
Corriendogem install mongrel Funcionó bien y aparentemente instalado mestizo también. Estoy un poco desconcertado porque:

script / server inicia webrick por defectowhich mongrel no devuelve nadalocate mongrel devuelve un montón de entradas como
/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
.
.
.

Parece que tengo mongrel instalado (tanto la instalación predeterminada como mi instalación personalizada). Entonces, ¿por qué no, qué mestizo devuelve algo?

También tratando de reinstalar el mestizo usandogem install mongrel devuelve lanza su propio conjunto de excepciones:

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

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