[WIP] Fix UIA path for elements within an Alert's view

There is a missing element that appears in the UIA path that is being trimmed in Subliminal. This change is needed in order to find elements in an alert window. I'm not sure if my solution is acceptable of comparing against the class name of _UIModalItemAlertContentView as a string.

The reason for doing this is because we have two alerts that pop up back to back in a particular case. When this happens, we need to ensure that the alerts are handled in a specific order, as the second alert pops in front of the first one while UIA is trying to tap on the first one. This leads to a timing issue and causes the tests to fail randomly. Ignoring the first alert and handling it manually seemed like a simpler solution than trying to modify the alert handler's behavior to respect insertion order.
I just posted a another potential fix that doesn't require the reference to the private class. The minimum UIA path would be:

Target -> Alert Window -> Alert View -> Table View -> Table Cell

The "Alert View" is really the _UIModalItemAlertContentView and is the one required element not making it into the accessibility path. However, leaving all UIView's in the path in this case seems to work fine as well. I'm testing this on iOS 6 now to make sure it works in general.

This is what the alert window hierarchy contains:
`
<_UIModalItemHostingWindow: 0x14815d70; frame = (0 0; 320 568)>
  | <UIView: 0x14815a60; frame = (0 0; 320 568)>
  | <UIView: 0x18336af0; frame = (0 0; 320 568)>
  |   | <UIView: 0x183573b0; frame = (0 0; 320 568)>
  |   | <_UIModalItemRepresentationView: 0x183565c0; frame = (25 212.5; 270 143)>
  |   |   | <_UIModalItemAlertBackgroundView: 0x1832cfb0; frame = (25 212.5; 270 143)>
  |   |   |   | <_UIBackdropView: 0x183487d0; frame = (25 212.5; 270 143)>
  |   |   |   |   | <_UIBackdropEffectView: 0x18322b10; frame = (25 212.5; 270 143)>
  |   |   |   |   | <UIView: 0x183383b0; frame = (25 212.5; 270 143)>
  |   |   |   | <UIImageView: 0x183455a0; frame = (25 212.5; 270 143); traits = (Image)>
  |   |   | <_UIModalItemAlertContentView: 0x148150a0; frame = (25 212.5; 270 143)>
  |   |   |   | <UITableView: 0x11a94c00; frame = (25 311.5; 270 44); label = 'Empty list'>
  |   |   |   |   + <UITableViewCellAccessibilityElement: 0x1835b470; frame = (25 311.5; 270 44); label = 'OK'; traits = (Button); accessibilityElement = YES>
  |   |   |   |   +   + <UITableTextAccessibilityElement: 0x18325260; frame = (25 311.5; 270 44); label = 'OK'; traits = (Button, Static Text); accessibilityElement = YES>
  |   |   |   |   | <UITableViewWrapperView: 0x1834cb20; frame = (25 311.5; 270 44)>
  |   |   |   |   |   | <_UIModalItemTableViewCell: 0x183504c0; frame = (25 311.5; 270 44); label = 'OK'; traits = (Button); accessibilityElement = YES>
  |   |   |   |   |   |   + <UITableTextAccessibilityElement: 0x18325260; frame = (25 311.5; 270 44); label = 'OK'; traits = (Button, Static Text); accessibilityElement = YES>
  |   |   |   |   |   |   | <UITableViewCellScrollView: 0x18357080; frame = (25 311.5; 270 44)>
  |   |   |   |   |   |   |   | <UITableViewCellContentView: 0x18345ef0; frame = (25 311.5; 270 43.5)>
  |   |   |   |   |   |   |   |   | <UILabel: 0x1834a8c0; frame = (40 311.5; 240 43.5); label = 'OK'; traits = (Static Text); accessibilityElement = YES>
  |   |   |   |   |   |   |   |   | <UIImageView: 0x10ef95c0; frame = (25 311.5; 0 0); traits = (Image)>
  |   |   |   |   | <UIImageView: 0x18357800; frame = (25 352; 270 3.5); traits = (Image)>
  |   |   |   |   | <UIImageView: 0x18357a50; frame = (291.5 311.5; 3.5 44); traits = (Image)>
  |   |   |   | <UIScrollView: 0x1834cf10; frame = (25 212.5; 270 80)>
  |   |   |   |   | <UILabel: 0x1834beb0; frame = (40 231.5; 240 21); label = 'Error'; traits = (Static Text); accessibilityElement = YES>
  |   |   |   |   | <UILabel: 0x1834c310; frame = (40 256.5; 240 36); label = 'That email is already taken. Please enter another address.'; traits = (Static Text); accessibilityElement = YES>
  |   |   |   |   | <UIImageView: 0x18358fb0; frame = (25 289; 270 3.5); traits = (Image)>
  |   |   |   |   | <UIImageView: 0x183591e0; frame = (291.5 212.5; 3.5 80); traits = (Image)>
  |   |   |   | <UIView: 0x18355100; frame = (25 311; 270 0.5)>
`