Fix yanking the last line.

When the last line in an editor has no newline char at the end, yanking it
line-wise should append one. So the last char will not be dropped when
pasting it.
Vim keymap can be disabled temporarily.

Make CodeMirror to be easier integrated into other framework with global
keymap (e.g., IPython).
E.g.
CodeMirror.Vim.getVimGlobalState_().disable = true;
Then nokey will be handled. To re-enable it:
CodeMirror.Vim.getVimGlobalState_().disable = false;