Ruby » Ruby master

merges r24211 from trunk into ruby_1_9_1.¶

• lib/matrix.rb (Matrix#rank): revert a part of r20859 to avoid
  infinite loop. [Bug #1020]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@24291 b2dd03c8-39d4-4d8f-98ff-823fe69b080e