Ruby

• common.mk (capi): use -b option for doxygen. It disables stdout
  buffering and prevents wrong reordering between stdout and stderr
  even when the output of "make" is redirected.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@29008 b2dd03c8-39d4-4d8f-98ff-823fe69b080e