When installing Review Board, a bad dependency or other issue

initializing Django would result in a breakage that won't be noticed

until later in the process. This would result in a series of

installation steps that say ERROR, but continue on until an exception

was raised.
We now check for errors here, and immediately quit with a helpful

message so it doesn't appear that the database was created or other

steps were taken.

Hit this while doing some testing and got very confused trying to

install a site.
Fixed it with this patch and repeated the failed install. Saw the

error message instead of a supposed "successful installation"

followed by traceback.