Fix problem in concating filters
Fix problem in concating filters

The check whether we fully own a filter in compile_concat, and therefore
can modify it destructively, was wrong. Besides holding the only reference
to the filter, we also need to be holding the only reference to the value
wrapping the filter.

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