When splitting the tree, check that we are atthe right subtree
When splitting the tree, check that we are atthe right subtree

Without the check, spliting at a subtree just gobbles up trees without any
regard for what that tree is. This becmoes a problem in a sequence like
  [ COMMENT ] * . [ key FOO . store BAR ] *
when there is no comment, and therefore no subtree witha NULL label. A tree
with a single node matching FOO is wrongly split as if there was a COMMENT
(which, if it were there would have to have a NULL label)

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