Conflicts:
	lib/codemirror.js

It should duplicate for every selection, and for non-empty selections
only duplicate the selected text.

Also, wrap the command in an operation and use the head rather than
the anchor of the selections.

Issue #2334

Issue #2305

Use CreateInsertModeChanges to make a copy of the latest
insert mode changes in pushInsertModeChanges so that the
latest insert mode changes can safely be modified without
bashing previously recorded macros.

Fix the :register command and add unit tests. Add a fakeOpenNotification for matching the notification text.

Issue #2326

Issue #2326

Conflicts:
	lib/codemirror.js

Issue #2305

Issue #2305

It causes noticeable missinge scrollbar in some cases.

Closes #2317

pressing Ctrl-Space once starts the selection extension mode,
pressing it again cancels that

It was broken and confused.

Make the mode register a list of completable words instead.

Issue #2324

Since it's what you want most of the time, and easy to forget.

Issue #2305

Issue #2332

In Vim, defaults keymap cannot be unmapped. They must be explicityly
set to <NOP>. In this case we allow that because
user defined maps are stored in the same map as the defaults.

Closes #2331

If a line has widgets with heights, use them when estimating line height.

This prevents a .refresh() call from reverting to less accurate line
heights.

Issue #2305

Issue #2323

Require explicit turning on of history event merging.

Issue #2305