tests/test-addremove.t

make: switch the PYTHON default to `py.exe -3` on Windows

Python3 _is_ named `python.exe` on Windows, but that isn't necessarily on PATH
when installing from python.org.  I do happen to have a python.exe on PATH in
`$LOCALAPPDATA/Microsoft/WindowsApps`, but it appears to be 0 bytes (likely
because of permission issues), and doesn't run:

    $ python -V
     - Cannot open

Pulkit hit the same error as I did though, so it isn't just my system:

    $ make -C . local
    make: Entering directory `/home/Dell/repos/hg-committed`
    python setup.py  \
              build_py -c -d . \
              build_ext  -i \
              build_hgexe  -i \
              build_mo
     - Cannot openmake: *** [local] Error 1

The `py.exe` dispatcher lives in the Windows directory (so it is on PATH), looks
up the python.org installation, and invokes that interpreter directly.  I get a
warning with py39, but if it's our issue, it was an existing one:

    $ make -C .. local
    make: Entering directory `/c/Users/Matt/hg'
    py -3 setup.py  \
              build_py -c -d . \
              build_ext  -i \
              build_hgexe  -i \
              build_mo
    C:\Users\Matt\AppData\Local\Programs\Python\Python39\lib\site-packages\setuptools\distutils_patch.py:25:
        UserWarning: Distutils was imported before Setuptools. This usage is discouraged and may
        exhibit undesirable behaviors or errors. Please use Setuptools' objects directly or at least
        import Setuptools first.
      warnings.warn(

The end result is a py3 based hg.exe that annoyingly won't run because it can't
find python39.dll.  It will run tests (the ones without the `python3` shbang
line anyway), because the test runner adjusts PATH to include the python running
it.

Differential Revision: https://phab.mercurial-scm.org/D9361

  $ hg init rep
  $ cd rep
  $ mkdir dir
  $ touch foo dir/bar
  $ hg -v addremove
  adding dir/bar
  adding foo
  $ hg -v commit -m "add 1"
  committing files:
  dir/bar
  foo
  committing manifest
  committing changelog
  committed changeset 0:6f7f953567a2
  $ cd dir/
  $ touch ../foo_2 bar_2
  $ hg -v addremove
  adding dir/bar_2
  adding foo_2
  $ hg -v commit -m "add 2"
  committing files:
  dir/bar_2
  foo_2
  committing manifest
  committing changelog
  committed changeset 1:e65414bf35c5
  $ cd ..
  $ hg forget foo
  $ hg -v addremove
  adding foo
  $ hg forget foo

  $ hg -v addremove nonexistent
  nonexistent: $ENOENT$
  [1]

  $ cd ..

  $ hg init subdir
  $ cd subdir
  $ mkdir dir
  $ cd dir
  $ touch a.py
  $ hg addremove 'glob:*.py'
  adding a.py
  $ hg forget a.py
  $ hg addremove -I 'glob:*.py'
  adding a.py
  $ hg forget a.py
  $ hg addremove
  adding dir/a.py
  $ cd ..

  $ hg init sim
  $ cd sim
  $ echo a > a
  $ echo a >> a
  $ echo a >> a
  $ echo c > c
  $ hg commit -Ama
  adding a
  adding c
  $ mv a b
  $ rm c
  $ echo d > d
  $ hg addremove -n -s 50 # issue 1696
  removing a
  adding b
  removing c
  adding d
  recording removal of a as rename to b (100% similar)
  $ hg addremove -ns 50 --color debug
  [ui.addremove.removed ui.status|removing a]
  [ui.addremove.added ui.status|adding b]
  [ui.addremove.removed ui.status|removing c]
  [ui.addremove.added ui.status|adding d]
  [ ui.status|recording removal of a as rename to b (100% similar)]
  $ hg addremove -s 50
  removing a
  adding b
  removing c
  adding d
  recording removal of a as rename to b (100% similar)
  $ hg commit -mb
  $ cp b c
  $ hg forget b
  $ hg addremove -s 50
  adding b
  adding c

  $ rm c

  $ hg ci -A -m "c" nonexistent
  nonexistent: $ENOENT$
  abort: failed to mark all new/missing files as added/removed
  [255]

  $ hg st
  ! c
  $ cd ..