py3: use stringutil.pprint() to print NoneType

Before this patch, when running test-debugcommands.t, we get a TypeError because
NoneType can't be converted into bytes. This patch uses stringutil.pprint() to
print the ui._colormode.

We are now close to getting test-debugcommands.t passing on Python 3.

Differential Revision: https://phab.mercurial-scm.org/D3831

mercurial/debugcommands.py

@@ -427,7 +427,7 b' def debugcheckstate(ui, repo):'
         'hg debugcolor')
 def debugcolor(ui, repo, **opts):
     """show available color, effects or style"""
-    ui.write(('color mode: %s\n') % ui._colormode)
+    ui.write(('color mode: %s\n') % stringutil.pprint(ui._colormode))
     if opts.get(r'style'):
         return _debugdisplaystyle(ui)
     else:

tests/test-debugcommands.t

@@ -337,7 +337,7 b' Test debugcolor'
 
 #if no-windows
   $ hg debugcolor --style --color always | egrep 'mode|style|log\.'
-  color mode: ansi
+  color mode: 'ansi'
   available style:
   \x1b[0;33mlog.changeset\x1b[0m:                      \x1b[0;33myellow\x1b[0m (esc)
 #endif