Ensure fsi prompt is readonly
Correct range-check for emacs support

Previously the last line would be thought to be out of range by
fsautocomplete
Merge pull request #573 from 7sharp9/master

Added hotfix commits from vnext-release to fix bugzilla 20102
Merge pull request #572 from rneatherway/read-only-fsi

Ensure fsi prompt is readonly
Merge pull request #571 from rneatherway/emacslastline

Correct range-check for emacs support