Try to make more like rdebug. Get M-up/M-down working.  Need to revisit this code and rdebug-core to understand, unify, and simplify more.
Try to make more like rdebug. Get M-up/M-down working. 
Need to revisit this code and rdebug-core to understand, unify, and simplify
more.


git-svn-id: 7ffbd09614c8d739a966cfae413e2c1c0f4cb91b@732 453b2852-3d18-0410-866e-d09c099698e4

ruby-debug/ruby-debug-extra,ruby-debug/ruby-debug-extra