setup: fix py2exe generation broken by c3a6ec304055 (issue3116)

Py2exe is patching default distutils Distribution class. This patch ensures
that the right one is taken when calling hgdist class.

setup.py

@@ -121,6 +121,8 b' def hasfunction(cc, funcname):'
 try:
     import py2exe
     py2exeloaded = True
+    # import py2exe's patched Distribution class
+    from distutils.core import Distribution
 except ImportError:
     py2exeloaded = False