Checking for MutationObserver not in global

At the moment the scheduler checks MutationObserver and then assigning global.MutationObserver - causes a lot of fun in IE 11 extensions.
track active domain for nextTick for node.js 0.10.xx.

Closes #124
Release v1.0.8
Merge branch 'master' of github.com:petkaantonov/bluebird