An error occurred while installing mongrel (1.1.5), and Bundler cannot continue.

Installing mongrel (1.1.5) with native extensions 
Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

        /home/sachin/.rvm/rubies/ruby-1.9.3-p286/bin/ruby extconf.rb 
checking for main() in -lc... yes
creating Makefile

make
compiling http11_parser.c
compiling http11.c
http11.c: In function ‘http_field’:
http11.c:70:3: warning: format not a string literal and no format arguments [-Wformat-security]
http11.c:71:3: warning: format not a string literal and no format arguments [-Wformat-security]
http11.c:77:22: error: ‘struct RString’ has no member named ‘ptr’
http11.c:77:50: error: ‘struct RString’ has no member named ‘len’
http11.c: In function ‘request_uri’:
http11.c:102:3: warning: format not a string literal and no format arguments [-Wformat-security]
http11.c: In function ‘fragment’:
http11.c:113:3: warning: format not a string literal and no format arguments [-Wformat-security]
http11.c: In function ‘request_path’:
http11.c:124:3: warning: format not a string literal and no format arguments [-Wformat-security]
http11.c: In function ‘query_string’:
http11.c:135:3: warning: format not a string literal and no format arguments [-Wformat-security]
http11.c: In function ‘header_done’:
http11.c:172:33: error: ‘struct RString’ has no member named ‘ptr’
http11.c:174:89: error: ‘struct RString’ has no member named ‘ptr’
http11.c:176:52: error: ‘struct RString’ has no member named ‘ptr’
http11.c:177:26: error: ‘struct RString’ has no member named ‘len’
http11.c: In function ‘HttpParser_execute’:
http11.c:298:23: error: ‘struct RString’ has no member named ‘ptr’
http11.c:299:23: error: ‘struct RString’ has no member named ‘len’
http11.c:307:5: warning: format not a string literal and no format arguments [-Wformat-security]
make: *** [http11.o] Error 1


Gem files will remain installed in /home/sachin/.rvm/gems/ruby-1.9.3-p286@prjct/gems/mongrel-1.1.5 for inspection.
Results logged to /home/sachin/.rvm/gems/ruby-1.9.3-p286@prjct/gems/mongrel-1.1.5/ext/http11/gem_make.out
An error occurred while installing mongrel (1.1.5), and Bundler cannot continue.
Make sure that `gem install mongrel -v '1.1.5'` succeeds before bundling.

Solution:
change in Gemfile

gem "mongrel", ">= 1.2.0.pre2"