Vendored Version of Rack removed from 2-3-stable

It is possible to run Rails without separately installing a version of Rack with 2.3.2, with 2-2-stable, and with master, but not with 2-3-stable. This was explicitly removed with the following commit:

16f36b6171c855dcc92ef557c454fcfc314b617f

The attached bash shell script reproduces the problem; summary reproduced below:

Summary:
  origin/master                            pass
  origin/2-2-stable                        pass
  origin/2-3-stable                        fail
  16f36b6171c855dcc92ef557c454fcfc314b617f fail
  2d9b45722c5639ad822f9a213edfd4d2bb084dcb pass