init: turn on demandimport for Python 3.6 and above

This uses the new demandimport implementation for Python 3 introduced in
previous patches.

This doesn't yet enhance performance because it isn't integrated with the
custom source file loader we use on Python 3. We'll integrate the two in
upcoming patches.

hg

@@ -1,45 +1,45
 #!/usr/bin/env python
 #
 # mercurial - scalable distributed SCM
 #
 # Copyright 2005-2007 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 import os
 import sys
 
 if os.environ.get('HGUNICODEPEDANTRY', False):
     try:
         reload(sys)
         sys.setdefaultencoding("undefined")
     except NameError:
         pass
 
 libdir = '@LIBDIR@'
 
 if libdir != '@' 'LIBDIR' '@':
     if not os.path.isabs(libdir):
         libdir = os.path.join(os.path.dirname(os.path.realpath(__file__)),
                               libdir)
         libdir = os.path.abspath(libdir)
     sys.path.insert(0, libdir)
 
 # enable importing on demand to reduce startup time
 try:
-    if sys.version_info[0] < 3:
-        from mercurial import demandimport; demandimport.enable()
+    if sys.version_info[0] < 3 or sys.version_info >= (3, 6):
+        import hgdemandimport; hgdemandimport.enable()
 except ImportError:
     sys.stderr.write("abort: couldn't find mercurial libraries in [%s]\n" %
                      ' '.join(sys.path))
     sys.stderr.write("(check your install and PYTHONPATH)\n")
     sys.exit(-1)
 
 import mercurial.util
 import mercurial.dispatch
 
 for fp in (sys.stdin, sys.stdout, sys.stderr):
     mercurial.util.setbinary(fp)
 
 mercurial.dispatch.run()