Here are the steps you need to get ruby-debug to work with Ruby 1.9.3p125 in the Spree sandbox.
Setup
rvm 1.10.3
ruby 1.9.3p125
Spree 1.0.x
Installing Gems
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# download the source code for pre-release version of linecache, then install locallycurl-OLhttp://rubyforge.org/frs/download.php/75414/linecache19-0.5.13.gemgeminstalllinecache19-0.5.13.gem# download the source code for pre-release version of debug-base, then install locally# using rvm installed source code (/Users/cmar/.rvm/rubies/ruby-1.9.3-p125/rubies/src)curl-OLhttp://rubyforge.org/frs/download.php/75415/ruby-debug-base19-0.11.26.gemgeminstallruby-debug-base19-0.11.26.gem----with-ruby-include="${MY_RUBY_HOME/rubies/src}"