Added pullFile support for iOS simulator.

`mobile: pullFile {:path => '/Some/Path'}` fetches a file relative to
the root of the device's filesystem.

`mobile: pullFile {:path => '/Applications/Some.app'}` fetches a file
relative to the root of that Application's .app directory, adding in the
GUID.

Fixes #2010, #1807
Merge pull request #2227 from DylanLacey/get_docs

Added pullFile support for iOS simulator.