Update debugger and timecop gems for 1.9.3-p448

the debugger gem needs to know about your version of Ruby or it fails to
install. The version previously in Gemfile.lock didn't know about
1.9.3-p448. This one does...

TimeCop stopped working with 1.9.3-p448, or with current
ActiveSupport::TimeWithZone, updated to fix that too.