lib/pathname.rb: Backport #2110 [ruby-core:25627]; backport of r23093 to handle the scenario where, on filesystems like Windows', paths are compared using casecmp instead of ==.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8_6@28234 b2dd03c8-39d4-4d8f-98ff-823fe69b080e