gendoc: use real ui in place of stdout

ui attributes will be required by a help function, so a file object can't be
used as a fake ui.

doc/gendoc.py

@@ -14,6 +14,7 b' from mercurial.commands import table, gl'
 from mercurial.i18n import gettext, _
 from mercurial.help import helptable, loaddoc
 from mercurial import extensions
+from mercurial import ui as uimod
 
 def get_desc(docstr):
     if not docstr:
@@ -198,7 +199,8 b' if __name__ == "__main__":'
     if len(sys.argv) > 1:
         doc = sys.argv[1]
 
+    ui = uimod.ui()
     if doc == 'hg.1.gendoc':
-        showdoc(sys.stdout)
+        showdoc(ui)
     else:
-        showtopic(sys.stdout, sys.argv[1])
+        showtopic(ui, sys.argv[1])