Interfaces: accept options containing '_'
Interfaces: accept options containing '_'

Bug reported by Jonas Eriksson

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