Improvements to content assist for node.js buffer globals.  Fixes bug 418356

Signed-off-by: Manu Sridharan <msridhar@us.ibm.com>
[Bug 418385] Content Assist: fix jiggling of selected proposal text
Update node README
Bug 418365 - Editor page: Right pane keeps "find next" when left pane has selection changed (comment#3)