* sample/tkextlib/treectrl/explorer.rb: File.executable? returns true
    even if it's plain text file. (this function only checks access right)

again.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@8296 b2dd03c8-39d4-4d8f-98ff-823fe69b080e