check we can launch a device based on user's caps and throw a nice error if not (fix #2114)
Merge pull request #2223 from jlipps/master

check that iOS deviceName matches instruments's list before launching
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