Facebook iOS SDK 3.5.1

Summary:
    Bug fixes. See https://developers.facebook.com/ios/change-log-3.x/

Reviewed By: jacl

Test Plan: Release Testing.
Fix some namespace pollution in the static library.

This fixes namespace pollution, to prevent linker issues with apps and other
libraries with global symbols named eg. "kSDK".
Prefix defaultResultsLimit and defaultRadius.

These symbols are exported into the static library, so make sure they're prefixed
to avoid namespace collisions.
Update src/FBDataDiskCache.m

'DISPATCH_QUEUE_PRIORITY_BACKGROUND' is not supported in iOS 4.0, only 5.0. It has been changed to 'DISPATCH_QUEUE_PRIORITY_LOW'
Add a search bar
Fix method name such that the analyzer doesn't throw
Need to take a copy of the stack allocated block
Always renew the access token as we can never know if we're old or not