[e] (0) Improve cross-references aroung globalCompositeOperation

git-svn-id: https://svn.whatwg.org/webapps@8812 340c8d12-0b0e-0410-8428-c7bf67bfef74
[e] (0) Remove a note about a possible canvas change, since it hasn't happened for a few years now.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=26834
Affected topics: Canvas, HTML

git-svn-id: https://svn.whatwg.org/webapps@8813 340c8d12-0b0e-0410-8428-c7bf67bfef74
[giow] (3) getSVGDocument() can return null (IDL fix).
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=25940
Affected topics: DOM APIs

git-svn-id: https://svn.whatwg.org/webapps@8814 340c8d12-0b0e-0410-8428-c7bf67bfef74
Merge remote branch 'origin/master' into whatwg