Variable "source" wrongly used instead of "arg" in exception in source.rb

[mrj]

Line 20 of source.rb should be:

 raise "#{arg.class} is not a valid input stream.  It must walk \n"+

The current use of "source.class" gives error

undefined local variable or method `source' for REXML::SourceFactory:Class

[ser]

Fixed by changeset:1266