Update isolate documentation.
Update isolate documentation.

Currently it's not possible to control the spawned isolate through the
Isolate instance. -> Don't say so in the documentation.

BUG= http://dartbug.com/15150
R=lrn@google.com

Review URL: https://codereview.chromium.org//78223003

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@30528 260f80e4-7a28-3924-810f-c04153c831b5

dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk