Work around IE bug where drag events get fired twice

Closes #1551
[javascript mode] More comma-handling tweaks

Issue #1443
[xml-hint demo] Fix minor bug, add sponsor link
[xml-hint addon] Properly support single-quoted attributes
Remove setDragImage call for Safari (again)

Issue #332
[xml-hint demo] Disable implicit completion on single candidate

When implicitly activating completion, it is undesirable.
Fix partial-updating of lines with line widgets above them

Issue #1554
Merge branch 'master' of https://github.com/marijnh/CodeMirror
Merge branch 'master' of https://github.com/jessegrosjean/CodeMirror