Exclusives bugfix.
Exclusives bugfix.

Builds with no exclusives would sometimes fail due to a bug
in how execution order was planned.

Auditors: benjy

(sapling split of 4891bd7998e6ea1db44652c1e54360f20043fdbb)
di0spyr0s/pants,UnrememberMe/pants,foursquare/pants,sameerparekh/pants,tdyas/pants,dgomez10/xanon,qma/pants,pantsbuild/pants,dturner-tw/pants,TansyArron/pants,ericzundel/pants,megaserg/pants,areitz/pants,dgomez10/xanon,pantsbuild/pants,sameerparekh/pants,scode/pants,mateor/pants,cevaris/pants,jtrobec/pants,twitter/pants,baroquebobcat/pants,cevaris/pants,kwlzn/pants,baroquebobcat/pants,foursquare/pants,manasapte/pants,twitter/pants,sid-kap/pants,jtrobec/pants,wisechengyi/pants,peiyuwang/pants,Gabriel439/pants,pgroudas/pants,twitter/pants,UnrememberMe/pants,jsirois/pants,twitter/pants,pgroudas/pants,jessrosenfield/pants,benjyw/pants,UnrememberMe/pants,laurentgo/pants,slyphon/pants,15Dkatz/pants,UnrememberMe/pants,fkorotkov/pants,tejal29/pants,15Dkatz/pants,jessrosenfield/pants,UnrememberMe/pants,sameerparekh/pants,ity/pants,lahosken/pants,mateor/pants,fkorotkov/pants,Gabriel439/pants,sameerparekh/pants,lahosken/pants,megaserg/pants,slyphon/pants,gmalmquist/pants,digwanderlust/pants,areitz/pants,jtrobec/pants,sid-kap/pants,twitter/pants,laurentgo/pants,jsirois/pants,laurentgo/pants,15Dkatz/pants,peiyuwang/pants,areitz/pants,landism/pants,baroquebobcat/pants,pantsbuild/pants,wisechengyi/pants,ity/pants,TansyArron/pants,tdyas/pants,qma/pants,twitter/pants,pombredanne/pants,dturner-tw/pants,jessrosenfield/pants,landism/pants,kslundberg/pants,dgomez10/xanon,laurentgo/pants,kslundberg/pants,dturner-tw/pants,dgomez10/xanon,landism/pants,landism/pants,benjyw/pants,foursquare/pants,wisechengyi/pants,gmalmquist/pants,di0spyr0s/pants,peiyuwang/pants,wisechengyi/pants,cevaris/pants,tejal29/pants,tdyas/pants,wisechengyi/pants,megaserg/pants,ity/pants,dbentley/pants,jtrobec/pants,dbentley/pants,peiyuwang/pants,15Dkatz/pants,scode/pants,laurentgo/pants,15Dkatz/pants,ity/pants,sid-kap/pants,fkorotkov/pants,kwlzn/pants,pantsbuild/pants,fkorotkov/pants,dgomez10/xanon,peiyuwang/pants,tdyas/pants,tdyas/pants,dgomez10/xanon,foursquare/pants,manasapte/pants,dbentley/pants,dbentley/pants,jessrosenfield/pants,mateor/pants,tdyas/pants,sameerparekh/pants,slyphon/pants,manasapte/pants,areitz/pants,areitz/pants,ity/pants,lahosken/pants,pombredanne/pants,pantsbuild/pants,peiyuwang/pants,square/pants,landism/pants,dturner-tw/pants,fkorotkov/pants,mateor/pants,pombredanne/pants,Gabriel439/pants,ericzundel/pants,jtrobec/pants,gmalmquist/pants,lahosken/pants,square/pants,tdyas/pants,tejal29/pants,megaserg/pants,baroquebobcat/pants,qma/pants,Gabriel439/pants,UnrememberMe/pants,sid-kap/pants,pombredanne/pants,square/pants,TansyArron/pants,square/pants,dbentley/pants,di0spyr0s/pants,di0spyr0s/pants,benjyw/pants,laurentgo/pants,jessrosenfield/pants,mateor/pants,scode/pants,pombredanne/pants,wisechengyi/pants,pantsbuild/pants,dturner-tw/pants,dgomez10/xanon,kslundberg/pants,sid-kap/pants,UnrememberMe/pants,kwlzn/pants,digwanderlust/pants,pgroudas/pants,digwanderlust/pants,ericzundel/pants,pombredanne/pants,pgroudas/pants,mateor/pants,cevaris/pants,ericzundel/pants,tejal29/pants,pgroudas/pants,scode/pants,kwlzn/pants,ity/pants,landism/pants,kwlzn/pants,digwanderlust/pants,digwanderlust/pants,ity/pants,di0spyr0s/pants,foursquare/pants,ericzundel/pants,scode/pants,15Dkatz/pants,landism/pants,kslundberg/pants,dbentley/pants,gmalmquist/pants,cevaris/pants,tejal29/pants,gmalmquist/pants,wisechengyi/pants,dgomez10/xanon,peiyuwang/pants,TansyArron/pants,ericzundel/pants,dbentley/pants,qma/pants,dgomez10/xanon,fkorotkov/pants,megaserg/pants,tdyas/pants,Gabriel439/pants,baroquebobcat/pants,kslundberg/pants,qma/pants,ericzundel/pants,slyphon/pants,dturner-tw/pants,manasapte/pants,foursquare/pants,sid-kap/pants,tdyas/pants,ericzundel/pants,kslundberg/pants,cevaris/pants,wisechengyi/pants,twitter/pants,foursquare/pants,jessrosenfield/pants,mateor/pants,sameerparekh/pants,jessrosenfield/pants,baroquebobcat/pants,fkorotkov/pants,peiyuwang/pants,dturner-tw/pants,manasapte/pants,sameerparekh/pants,lahosken/pants,baroquebobcat/pants,pgroudas/pants,lahosken/pants,wisechengyi/pants,areitz/pants,sid-kap/pants,qma/pants,TansyArron/pants,scode/pants,foursquare/pants,TansyArron/pants,15Dkatz/pants,dgomez10/xanon,jtrobec/pants,megaserg/pants,twitter/pants,megaserg/pants,UnrememberMe/pants,kslundberg/pants,gmalmquist/pants,fkorotkov/pants,UnrememberMe/pants,benjyw/pants,pantsbuild/pants,Gabriel439/pants,baroquebobcat/pants,jtrobec/pants,manasapte/pants,benjyw/pants,cevaris/pants,gmalmquist/pants,slyphon/pants,manasapte/pants,areitz/pants,lahosken/pants,foursquare/pants,dgomez10/xanon,landism/pants,kwlzn/pants,mateor/pants,kwlzn/pants,twitter/pants,di0spyr0s/pants,slyphon/pants,15Dkatz/pants,jsirois/pants,pombredanne/pants,baroquebobcat/pants,lahosken/pants,TansyArron/pants,di0spyr0s/pants,slyphon/pants,Gabriel439/pants,benjyw/pants,benjyw/pants,scode/pants,qma/pants,digwanderlust/pants