[PATCH 7 of 9 pager] ui: add a debug print right before we start the pager

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1486443354 18000
#      Mon Feb 06 23:55:54 2017 -0500
# Node ID 277dab1428ca0e37b649b9cd980b1467cdfc85d0
# Parent  cfa569ed77883c41aecb3eaaa42876a5b0b7c52a
ui: add a debug print right before we start the pager

This makes it easier to figure out why a command is getting paginated.

diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -829,6 +829,7 @@ class ui(object):
             # interactive, the user didn't say HGPLAIN or
             # HGPLAINEXCEPT=pager, and the user didn't specify --debug.
             return
+        self.debug('starting pager for command %r\n' % command)
 
         # TODO: add a "system defaults" config section so this default
         # of more(1) can be easily replaced with a global