Fix an invalidation bug.
Fix an invalidation bug.

It was causing spurious invalidation, especially of ivy, where you'd build
successfully, change nothing at all, build again and ivy would re-resolve.

The problem was that were were treating Pants targets as things to
invalidate on, and they unfortunately have the same id as the target
they point to...

TODO: Get rid of Pants in the target graph. It exists only as a BUILD
file parsing construct, it shouldn't affect things later on.

Auditors: pl

(sapling split of 73053d8673438d01dec38408a9fedfcd2300b990)
qma/pants,foursquare/pants,foursquare/pants,laurentgo/pants,15Dkatz/pants,lahosken/pants,15Dkatz/pants,tdyas/pants,sameerparekh/pants,15Dkatz/pants,areitz/pants,wisechengyi/pants,foursquare/pants,landism/pants,lahosken/pants,landism/pants,kwlzn/pants,sid-kap/pants,slyphon/pants,pantsbuild/pants,jsirois/pants,pantsbuild/pants,foursquare/pants,megaserg/pants,jessrosenfield/pants,sameerparekh/pants,megaserg/pants,tdyas/pants,benjyw/pants,kslundberg/pants,areitz/pants,twitter/pants,areitz/pants,square/pants,wisechengyi/pants,jtrobec/pants,square/pants,di0spyr0s/pants,dbentley/pants,benjyw/pants,lahosken/pants,TansyArron/pants,ericzundel/pants,kslundberg/pants,baroquebobcat/pants,tdyas/pants,ericzundel/pants,foursquare/pants,Gabriel439/pants,ericzundel/pants,peiyuwang/pants,cevaris/pants,landism/pants,TansyArron/pants,ericzundel/pants,ericzundel/pants,square/pants,pantsbuild/pants,twitter/pants,manasapte/pants,TansyArron/pants,twitter/pants,megaserg/pants,dbentley/pants,pgroudas/pants,tejal29/pants,peiyuwang/pants,Gabriel439/pants,mateor/pants,benjyw/pants,sid-kap/pants,pgroudas/pants,wisechengyi/pants,lahosken/pants,laurentgo/pants,wisechengyi/pants,lahosken/pants,pantsbuild/pants,slyphon/pants,Gabriel439/pants,ity/pants,pgroudas/pants,di0spyr0s/pants,lahosken/pants,dgomez10/xanon,UnrememberMe/pants,15Dkatz/pants,jessrosenfield/pants,dturner-tw/pants,mateor/pants,kslundberg/pants,tdyas/pants,foursquare/pants,dturner-tw/pants,sameerparekh/pants,mateor/pants,dgomez10/xanon,digwanderlust/pants,ericzundel/pants,TansyArron/pants,jessrosenfield/pants,jsirois/pants,sid-kap/pants,15Dkatz/pants,landism/pants,areitz/pants,tdyas/pants,cevaris/pants,pgroudas/pants,pombredanne/pants,mateor/pants,wisechengyi/pants,kwlzn/pants,dbentley/pants,gmalmquist/pants,baroquebobcat/pants,dgomez10/xanon,jtrobec/pants,kwlzn/pants,UnrememberMe/pants,peiyuwang/pants,dbentley/pants,kwlzn/pants,digwanderlust/pants,sameerparekh/pants,dturner-tw/pants,peiyuwang/pants,baroquebobcat/pants,mateor/pants,baroquebobcat/pants,sid-kap/pants,di0spyr0s/pants,tdyas/pants,sid-kap/pants,fkorotkov/pants,digwanderlust/pants,peiyuwang/pants,laurentgo/pants,fkorotkov/pants,UnrememberMe/pants,sid-kap/pants,slyphon/pants,di0spyr0s/pants,twitter/pants,gmalmquist/pants,megaserg/pants,mateor/pants,ericzundel/pants,laurentgo/pants,pombredanne/pants,twitter/pants,ity/pants,benjyw/pants,dturner-tw/pants,tdyas/pants,dgomez10/xanon,landism/pants,mateor/pants,manasapte/pants,pombredanne/pants,Gabriel439/pants,manasapte/pants,digwanderlust/pants,cevaris/pants,scode/pants,pantsbuild/pants,manasapte/pants,kslundberg/pants,ity/pants,UnrememberMe/pants,twitter/pants,lahosken/pants,Gabriel439/pants,manasapte/pants,fkorotkov/pants,baroquebobcat/pants,di0spyr0s/pants,jtrobec/pants,areitz/pants,jtrobec/pants,TansyArron/pants,baroquebobcat/pants,cevaris/pants,Gabriel439/pants,qma/pants,scode/pants,dgomez10/xanon,pgroudas/pants,tdyas/pants,tdyas/pants,manasapte/pants,wisechengyi/pants,mateor/pants,TansyArron/pants,digwanderlust/pants,twitter/pants,gmalmquist/pants,scode/pants,jessrosenfield/pants,pantsbuild/pants,tejal29/pants,jtrobec/pants,pombredanne/pants,UnrememberMe/pants,scode/pants,dturner-tw/pants,twitter/pants,scode/pants,lahosken/pants,qma/pants,slyphon/pants,dbentley/pants,fkorotkov/pants,jessrosenfield/pants,gmalmquist/pants,wisechengyi/pants,fkorotkov/pants,slyphon/pants,pombredanne/pants,dturner-tw/pants,megaserg/pants,UnrememberMe/pants,qma/pants,dgomez10/xanon,Gabriel439/pants,pantsbuild/pants,slyphon/pants,landism/pants,qma/pants,benjyw/pants,foursquare/pants,qma/pants,15Dkatz/pants,laurentgo/pants,pgroudas/pants,scode/pants,tejal29/pants,sameerparekh/pants,tejal29/pants,slyphon/pants,di0spyr0s/pants,wisechengyi/pants,jtrobec/pants,kwlzn/pants,fkorotkov/pants,ity/pants,dgomez10/xanon,fkorotkov/pants,peiyuwang/pants,landism/pants,dgomez10/xanon,dgomez10/xanon,laurentgo/pants,baroquebobcat/pants,dgomez10/xanon,kwlzn/pants,kslundberg/pants,scode/pants,UnrememberMe/pants,ericzundel/pants,areitz/pants,kwlzn/pants,benjyw/pants,square/pants,qma/pants,dgomez10/xanon,gmalmquist/pants,foursquare/pants,UnrememberMe/pants,areitz/pants,sameerparekh/pants,twitter/pants,jessrosenfield/pants,15Dkatz/pants,kslundberg/pants,foursquare/pants,fkorotkov/pants,sameerparekh/pants,ity/pants,dbentley/pants,benjyw/pants,dturner-tw/pants,cevaris/pants,gmalmquist/pants,pombredanne/pants,UnrememberMe/pants,di0spyr0s/pants,tejal29/pants,baroquebobcat/pants,kslundberg/pants,wisechengyi/pants,ity/pants,jessrosenfield/pants,TansyArron/pants,pombredanne/pants,baroquebobcat/pants,gmalmquist/pants,dbentley/pants,peiyuwang/pants,jsirois/pants,digwanderlust/pants,cevaris/pants,megaserg/pants,megaserg/pants,peiyuwang/pants,sid-kap/pants,15Dkatz/pants,cevaris/pants,landism/pants,jtrobec/pants,ity/pants,manasapte/pants