Merge pull request #1280 from ricksladkey/fixes-external-select

Use 'selectmode=mouse' setting for external selects
Merge pull request #1282 from ricksladkey/fixes-select-undo

Add Ctrl+A to select mode and fix undo replacing selection
Merge pull request #1279 from ricksladkey/fixes-line-undo

Add support for the 'U' command (undo latest changes on one line)
Use native caret height for VsVim caret height

Fixes #1242.
Merge remote-tracking branch 'upstream/master'
Merge branch 'fixes-1242'