Added a support script to check for files missing in CMake.
Added a support script to check for files missing in CMake.

This compares the sources listed in the Autotools and CMake build
files, and emits the difference. We use this to check if the builds
have diverged, and how to reconcile that divergence.

Review: https://reviews.apache.org/r/67707/

chhsia0/mesos,reneploetz/mesos,kaysoky/mesos,andschwa/mesos,abudnik/mesos,chhsia0/mesos,abudnik/mesos,Gilbert88/mesos,gsantovena/mesos,jpeach/mesos,kaysoky/mesos,gsantovena/mesos,dforsyth/mesos,reneploetz/mesos,gsantovena/mesos,Gilbert88/mesos,jpeach/mesos,Gilbert88/mesos,gsantovena/mesos,kaysoky/mesos,dforsyth/mesos,abudnik/mesos,reneploetz/mesos,kaysoky/mesos,andschwa/mesos,Gilbert88/mesos,andschwa/mesos,andschwa/mesos,Gilbert88/mesos,andschwa/mesos,dforsyth/mesos,gsantovena/mesos,abudnik/mesos,gsantovena/mesos,gsantovena/mesos,kaysoky/mesos,jpeach/mesos,jpeach/mesos,kaysoky/mesos,andschwa/mesos,jpeach/mesos,dforsyth/mesos,reneploetz/mesos,Gilbert88/mesos,chhsia0/mesos,reneploetz/mesos,chhsia0/mesos,reneploetz/mesos,kaysoky/mesos,abudnik/mesos,Gilbert88/mesos,dforsyth/mesos,chhsia0/mesos,reneploetz/mesos,andschwa/mesos,jpeach/mesos,jpeach/mesos,chhsia0/mesos,dforsyth/mesos,abudnik/mesos,dforsyth/mesos,abudnik/mesos,chhsia0/mesos