Temporary workaround for use of purged ID in updateComponent

Would this be an acceptable temporary workaround for #1569 @sebmarkbage? Seeing as the alternative seems to be quite an extensive refactor, which may not come any time soon.

With this PR and #1568 (which is straightforward) it would be possible to go ahead with my #1570 PR (remove reactid from DOM) when you guys have reviewed it and decided whether you prefer lazy/immediate traversal.