augtool: change readline tab completion to be context-aware
augtool: change readline tab completion to be context-aware

jasperla/augeas,dafugg/augeas,hercules-team/augeas,kunkku/augeas,kunkku/augeas,GeoffWilliams/augeas,hercules-team/augeas-do-not-use,jtopjian/augeas,jjlin/augeas,lutter/augeas,kunkku/augeas,mchf/augeas,jjlin/augeas,manandbytes/augeas,kumy/augeas,MikaelSmith/augeas,jjlin/augeas,domcleal/augeas,raphink/augeas,manandbytes/augeas,raphink/augeas,domcleal/augeas,kumy/augeas,jasperla/augeas,hercules-team/augeas-do-not-use,pevalme/augeas,kumy/augeas,mlichvar/augeas,ptoscano/augeas,ptoscano/augeas,mchf/augeas,jtopjian/augeas,kumy/augeas,mlichvar/augeas,MikaelSmith/augeas,lutter/augeas,hercules-team/augeas-do-not-use,pevalme/augeas,pevalme/augeas,ptoscano/augeas,dafugg/augeas,domcleal/augeas,dafugg/augeas,mlichvar/augeas,lutter/augeas,hercules-team/augeas,GeoffWilliams/augeas