tests/test-merge8.t

packaging: extract py2exe functionality to own module

py2exe builds are shared between Inno Setup and WIX. We'll
want the logic for performing py2exe builds to be reusable
across the code for both installers.

This commit extracts the py2exe-specific functionality into
its own module.

There's definitely room to customize things further. This will
be done in future commits, as necessary. (I'm not even sure what
customizations WIX will require yet. Presumably a lot.)

Differential Revision: https://phab.mercurial-scm.org/D6091

Test for changeset ba7c74081861
(update dirstate correctly for non-branchmerge updates)
  $ hg init a
  $ cd a
  $ echo a > a
  $ hg add a
  $ hg commit -m a
  $ cd ..
  $ hg clone a b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd a
  $ hg mv a b
  $ hg commit -m move
  $ echo b >> b
  $ hg commit -m b
  $ cd ../b
  $ hg pull ../a
  pulling from ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 1 files
  new changesets e3c9b40284e1:772b37f1ca37
  (run 'hg update' to get a working copy)
  $ hg update
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ cd ..