Install and upgrade show errors

[ringmaster]

From wp-testers:

Actually see this in both install.php and upgrade.php using 2.1-alpha1

Warning: array_keys() [function.array-keys]: The first argument should be an
array in C:\xampp\htdocs\wp21\wp-includes\functions.php on line 2360

Warning: array_shift() [function.array-shift]: The argument should be an
array in C:\xampp\htdocs\wp21\wp-includes\functions.php on line 2360

Warning: Invalid argument supplied for foreach() in
C:\xampp\htdocs\wp21\wp-includes\functions.php on line 2365

Michael E. Hancock

Since wp_cron() is called from shutdown, it executes during the install and upgrade. If the "crons" option doesn't already exist, it generates errors.

The attached patch cleans things up.

[ringmaster]

Cleans up wp_cron()

[ryan]

(In [3522]) wp_cron() array warning fix ups from Owen. fixes #2436