Set $rootElement sooner during injector bootstrap.

It's valid (though perhaps ill-advised) for directives to access
$rootElement during initialization, so we need to make it available
before compilation.
Don't try to digest in injector.bootstrap.

Although angular.bootstrap digests to make its compilation take effect,
it's not appropriate for injector.bootstrap to do so since it may be run
from code that's already inside a digest cycle. It is the caller's
responsibility when bootstraping to run digest at an appropriate time.
Change version to 0.0.17 for release.