Move getters from Options to Platform

The getters for executable, script and version are now statics on
Platform. I kept them on Options for now, but updated most tests to
use Platform.

R=ajohnsen@google.com, floitsch@google.com, iposva@google.com
BUG=

Review URL: https://codereview.chromium.org//17406010

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@24401 260f80e4-7a28-3924-810f-c04153c831b5