tests/test-mactext.t

automation: always use latest Windows AMI

The old AMI isn't available any more.

We seem to run into this problem every few months. Amazon (or
Microsoft) appears to be removing the old AMIs when they are
superseded or something. Let's give up on tracking known images
and switch the image selection logic to use the latest published
image.

Differential Revision: https://phab.mercurial-scm.org/D8465

  $ cat > unix2mac.py <<EOF
  > import sys
  > 
  > for path in sys.argv[1:]:
  >     data = open(path, 'rb').read()
  >     data = data.replace(b'\n', b'\r')
  >     open(path, 'wb').write(data)
  > EOF
  $ hg init
  $ echo '[hooks]' >> .hg/hgrc
  $ echo 'pretxncommit.cr = python:hgext.win32text.forbidcr' >> .hg/hgrc
  $ echo 'pretxnchangegroup.cr = python:hgext.win32text.forbidcr' >> .hg/hgrc
  $ cat .hg/hgrc
  [hooks]
  pretxncommit.cr = python:hgext.win32text.forbidcr
  pretxnchangegroup.cr = python:hgext.win32text.forbidcr

  $ echo hello > f
  $ hg add f
  $ hg ci -m 1

  $ "$PYTHON" unix2mac.py f
  $ hg ci -m 2
  attempt to commit or push text file(s) using CR line endings
  in dea860dc51ec: f
  transaction abort!
  rollback completed
  abort: pretxncommit.cr hook failed
  [255]
  $ hg cat f | f --hexdump
  
  0000: 68 65 6c 6c 6f 0a                               |hello.|
  $ f --hexdump f
  f:
  0000: 68 65 6c 6c 6f 0d                               |hello.|