fix debug running on 1.8.7

Author: denofevil

lib/ruby-debug-ide.rb

@@ -109,7 +109,7 @@ def debug_program(options)
         @proceed.wait(@mutex)
       end
 
-      abs_prog_script = File.absolute_path(Debugger::PROG_SCRIPT)
+      abs_prog_script = File.expand_path(Debugger::PROG_SCRIPT)
       bt = debug_load(abs_prog_script, options.stop, options.load_mode)
       if bt && !bt.is_a?(SystemExit)
         $stderr.print bt.backtrace.map{|l| "\t#{l}"}.join("\n"), "\n"