Added custom error class and tastypie transaction middleware
Return the serialzed version
Added more status codes
Remvoed HttpErrorResponse class. Using status_codes
Merge branch 'upstream' into transaction_middleware

Conflicts:
	tastypie/http.py
Tests for the TransactionMiddleware
added docs
Merge branch 'vbabiy-transaction_middleware' into 7geese-tastypie-v2