Avoid scrolling prior to attribute query.

Modify GetAttributeNHandler to avoid scrolling prior to attribute query,
in order to preserve element coordinates.
Improve diagnostics.
Make safari startup more robust on iOS 7.

The default favorites in the iOS 7 home screen where creating random
crashes of Safari when starting on slow machines or when the network was
slow. Replaced the default favories with a single "about:blank" entry.
Make some messages more user-friendly.
Calculate the exact sdk version using xcodebuild.
Support native events for iOS 7.
Tune logging.
Handle special keys in iOS 7.
Fix the FormHandlingTests.