The evolving and evolved signals were being emitted within a

try/except, and if these had ended up raising an exception,

evolving_failed would end up being emitted as well. This could cause

some weirdness and broken behavior. We now emit these outside of the

signal handler instead.

Unit tests pass on all supported versions of Django.
Tested upgrading a database and hitting an error in the evolved

handler. Saw that evolving_failed did not get emitted (which caused

a weird breakage in testing).