test-debugextensions: sanitize JSON output for Windows

Windows is printing a double backslash, which isn't handled by (glob):

  --- c:/Users/Matt/Projects/hg/tests/test-debugextensions.t
  +++ c:/Users/Matt/Projects/hg/tests/test-debugextensions.t.err
  @@ -47,7 +47,7 @@
      {
       "buglink": "",
       "name": "color",
  -    "source": "*/hgext/color.pyc", (glob)
  +    "source": "c:\\Users\\Matt\\Projects\\hg\\hgext\\color.pyc",
       "testedwith": "internal"
      },
      {

tests/test-debugextensions.t

@@ -1,83 +1,83 b''
   $ hg debugextensions
 
   $ debugpath=`pwd`/extwithoutinfos.py
 
   $ cat > extwithoutinfos.py <<EOF
   > EOF
 
   $ cat >> $HGRCPATH <<EOF
   > [extensions]
   > color=
   > histedit=
   > patchbomb=
   > rebase=
   > mq=
   > ext1 = $debugpath
   > EOF
 
   $ hg debugextensions
   color
   ext1 (untested!)
   histedit
   mq
   patchbomb
   rebase
 
   $ hg debugextensions -v
   color
     location: */hgext/color.pyc (glob)
     tested with: internal
   ext1
     location: */extwithoutinfos.pyc (glob)
   histedit
     location: */hgext/histedit.pyc (glob)
     tested with: internal
   mq
     location: */hgext/mq.pyc (glob)
     tested with: internal
   patchbomb
     location: */hgext/patchbomb.pyc (glob)
     tested with: internal
   rebase
     location: */hgext/rebase.pyc (glob)
     tested with: internal
 
-  $ hg debugextensions -Tjson
+  $ hg debugextensions -Tjson | sed 's|\\\\|/|g'
   [
    {
     "buglink": "",
     "name": "color",
     "source": "*/hgext/color.pyc", (glob)
     "testedwith": "internal"
    },
    {
     "buglink": "",
     "name": "ext1",
     "source": "*/extwithoutinfos.pyc", (glob)
     "testedwith": ""
    },
    {
     "buglink": "",
     "name": "histedit",
     "source": "*/hgext/histedit.pyc", (glob)
     "testedwith": "internal"
    },
    {
     "buglink": "",
     "name": "mq",
     "source": "*/hgext/mq.pyc", (glob)
     "testedwith": "internal"
    },
    {
     "buglink": "",
     "name": "patchbomb",
     "source": "*/hgext/patchbomb.pyc", (glob)
     "testedwith": "internal"
    },
    {
     "buglink": "",
     "name": "rebase",
     "source": "*/hgext/rebase.pyc", (glob)
     "testedwith": "internal"
    }
   ]