rexml: Fix a XPath bug of $variable

[Bug #14600]
    
* lib/rexml/functions.rb: Fix a bug that "$variable" returns
  node instead of ndoe set.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63082 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rexml/xpath_parser.rb

@@ -375,7 +375,7 @@ module REXML
 
         when :variable
           var_name = path_stack.shift
-          return @variables[ var_name ]
+          return [@variables[var_name]]
 
         # :and, :or, :eq, :neq, :lt, :lteq, :gt, :gteq
         # TODO: Special case for :or and :and -- not evaluate the right