Adjustments to the previous commit
Uniformize slash_item() with item()
Fix #2558
Fix #2560
Form helper: refactor form_open() and _attributes_to_string()
More logical order
Merge pull request #2565 from vlakoff/develop

Form helper: refactor form_open() and _attributes_to_string()
Merge pull request #2554 from vlakoff/develop-3

config->item() now returns NULL instead of FALSE when the required item doesn't exist.
Complete 3.0 upgrade notes about NULL returned on missing items
Form helper _attributes_to_string() micro-optimization

As $attributes should be most of the times an array, let's save an is_string() call.
Polishing Form helper
Change spaces to tabs
Fix #2568
Merge pull request #2567 from vlakoff/develop-2

Polishing Form helper
Cache Log Error Levels
The log messages in the cache drvier's is_supported calls are more suited for the debug level.
Updated Changelog Cache Log Level
- Updated the changelog to include the log level updates in the cache drivers.
Merge pull request #2569 from refringe/develop

Cache Log Error Levels
Optimize CI_Session::__construct() routines and make driver validity check stricter
Add windows filename rule as an option for upload files
Revert "Add windows filename rule as an option for upload files"

This reverts commit 23719ab569c9c8d6b791f65d7861daba3895ddcb.