Show cause of error when opening drag-&-dropped files fails.
Plumb the error code back from the FILE_OPEN command, and display errors
in the existing bullet list error dialog used by DragAndDrop.
add link to troubleshooting page to live preview error messages
restore string
fix typo
Add unit test to verify that FILE_OPEN command now returns error code when
it fails.

Also, cleanup: group image-related tests into a single describe() instead
of a separate one per it().
Merge remote-tracking branch 'origin/master' into pflynn/dragdrop-errors

And clean up blank-line spacing in DocumentCommandHandlers-test
change for code review
Navigate through Extension Manager tabs via Ctrl-(Shift)-Tab
Remove unused vars
Add references to utils/Global back
Fix Travis failure
Fix "globals" option
Add "showCursorWhenSelecting" pref
Merge remote-tracking branch 'upstream/master' into unused-vars

Conflicts:
	src/brackets.js
	src/document/DocumentManager.js
	src/editor/EditorManager.js
	src/editor/ImageViewer.js
	src/extensions/default/JavaScriptQuickEdit/unittests.js
	src/extensions/default/UrlCodeHints/unittests.js
	src/language/CodeInspection.js
	src/project/WorkingSetSort.js
	src/project/WorkingSetView.js
	src/search/FindReplace.js
	src/search/ScrollTrackMarkers.js
	test/spec/FindReplace-test.js
	test/spec/LanguageManager-test.js
[SplitView] Removed unused vars
Fix EditorCommandHandlers unit tests
Update
Merge remote-tracking branch 'upstream/master' into unused-vars
bringing back the triangle (partly) to fix 9067
fix triangle protrusion issue 9035