升级到最新的mac os Mavericks。装json出现错误：
gem install json -v '1.8.1'
Building native extensions. This could take a while...
ERROR: Error installing json:
ERROR: Failed to build gem native extension.
/usr/local/var/rbenv/versions/2.0.0-p247/bin/ruby extconf.rb
creating Makefile
make "DESTDIR="
compiling generator.c
In file included from /usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby.h:33,
from ../fbuffer/fbuffer.h:5,
from generator.c:1:
/usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby/ruby.h:51:21: error: string.h: No such file or directory
/usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby/ruby.h:61:21: error: stdint.h: No such file or directory
/usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby/ruby.h:64:23: error: inttypes.h: No such file or directory
/usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby/ruby.h:68:19: error: stdio.h: No such file or directory
解决办法：
需要重新安装Command Line Developer Tools
如果这个办法还是不行，mac下需要安装下apple-gcc42
注意brew 0.9.4应该是不带apple-gcc42的源的，可以使用brew doctor检查下是否和Mavericks兼容，这里需要升级
