Flush command should allow to choose send/not send syncdb signal and call/not call loaddata command

[kapa77]

The flush command is sending syncdb signal at the end of it's run. It can be problematic with contenttype app installed. I have this situation:
I have old version of app with contentype app installed, I wrote new version of part of my project and now i want to dumpdata from old db and loaddata on new db.
There is script that ports data from old to new db. The problem id that i have generic relations and they have relation to content types, and when i run flush content type app is creating conten types in db but in different order than i have in my old db, and with this my generic relation are broken.

[Russell Keith-Magee]

At the core, this is really a duplicate of #7052. Changing the behaviour of flush isn't the solution. We need to fix the real problem - handling serialization and deserialization of data that is created dynamically during synchronization.