Fixed #22983: Alert when squashing RunPython operations with referred functions.
Bump the default iterations for PBKDF2.

The rate at which we've increased this has not been keeping up with hardware (and software) improvements, and we're now considerably behind where we should be. The delta between our performance and an optimized implementation's performance prevents us from improving that further, but hopefully once Python 2.7.8 and 3.4+ get into more hands we can more aggressively increase this number.
Removed extra newline.
Checked more precisely whether the app registry is ready.

Accounted for the three stages of population: app configs, models,
ready() methods of app configs.
Fixed #22939 -- Delayed admin_static backend detection

Thanks generalov for the report.