compatibility with ruby 1.9

[neigesdantan]

file soap4r-spox-1.6.0/lib/soap/mapping/mapping.rb needs some fixes:

obj.instance_variables inclusion is checked used strings. In ruby 1.9 Object#instance_variables returns an array of symbols so using Array#include? with a string parameter will always return false.

I propose to use the following fixes that will work in both ruby 1.9 and 1.8:

@line 256
ivars = obj.instance_variables.collect{|t| t.to_s}

@line 316
iv = obj.instance_variables.collect{|t| t.to_s}