Use the pager given by the environment to display long output

Unix systems usually have a PAGER environment variable set.
If it is set, mercurial will use the pager application to display
output.

Two configuration variables are available to influence the
behaviour of the pager:
  pager.application
    sets the application to be used
  pager.quiet
   silences Broken Pipe errors that might occur when the user
   quits the pager before mercurial finished to write the output

hgext/pager.py

@@ -0,0 +1,54 b''
+# pager.py - display output using a pager
+#
+# Copyright 2008 David Soria Parra <[e-mail]>
+#
+# This software may be used and distributed according to the terms
+# of the GNU General Public License, incorporated herein by reference.
+#
+# To load the extension add it to your .hgrc file
+#
+#   [extension]
+#   hgext.pager =
+#
+# To set the pager that should be used, set the application variable
+#
+#   [pager]
+#   application = less
+#
+# You can also set environment variables there
+#
+#   [pager]
+#   application = LESS='FSRX' less
+#
+# If no application is set, the pager extensions use the environment
+# variable $PAGER. If neither pager.application, nor
+# $PAGER is set, no pager is used.
+#
+# If you notice "BROKEN PIPE" error messages, you can disable them
+# by setting
+#
+#  [pager]
+#  quiet = True
+#
+
+import sys, os, signal
+
+def getpager(ui):
+    '''return a pager
+
+    We separate this method from the pager class as we don't want to
+    instantiate a pager if it is not used at all
+    '''
+    if sys.stdout.isatty():
+        return (ui.config("pager", "application")
+                or os.environ.get("PAGER"))
+
+def uisetup(ui):
+    # disable broken pipe error messages
+    if ui.configbool('pager', 'quiet', False):
+        signal.signal(signal.SIGPIPE, signal.SIG_DFL)
+
+    if getpager(ui):
+        pager = os.popen(getpager(ui), 'wb')
+        sys.stderr = pager
+        sys.stdout = pager