pager: Add a configuration to enable/disable the pager for certain commands

Add the configuration options pager.ignore and pager.attend.
You can disable the pager on certain commands by adding them to the
pager.ignore setting. To whitelist commands, you can add them to pager.attend.
To disable or enable global commands like 'hg version' or 'hg help'
you have to use your global .hgrc. (thanks, Matt Mackall)

hgext/pager.py

@@ -24,12 +24,37 b''
 #
 #   [pager]
 #   quiet = True
+#
+# You can disable the pager for certain commands by adding them to the
+# pager.ignore list:
+#
+#   [pager]
+#   ignore = version, help, update
+#
+# You can also enable the pager only for certain commands using pager.attend:
+#
+#   [pager]
+#   attend = log
+#
+# If pager.attend is present, pager.ignore will be ignored.
+#
+# To ignore global commands like 'hg version' or 'hg help', you have to specify them
+# in the global .hgrc
 
 import sys, os, signal
+from mercurial import dispatch
 
 def uisetup(ui):
-    p = ui.config("pager", "pager", os.environ.get("PAGER"))
-    if p and sys.stdout.isatty():
-        if ui.configbool('pager', 'quiet'):
-            signal.signal(signal.SIGPIPE, signal.SIG_DFL)
-        sys.stderr = sys.stdout = os.popen(p, "wb")
+    def pagecmd(ui, options, cmd, cmdfunc):
+        p = ui.config("pager", "pager", os.environ.get("PAGER"))
+        if p and sys.stdout.isatty():
+            attend = ui.configlist('pager', 'attend')
+            if (cmd in attend or
+                (cmd not in ui.configlist('pager', 'ignore') and not attend)):
+                sys.stderr = sys.stdout = os.popen(p, "wb")
+                if ui.configbool('pager', 'quiet'):
+                    signal.signal(signal.SIGPIPE, signal.SIG_DFL)
+        return oldrun(ui, options, cmd, cmdfunc)
+
+    oldrun = dispatch._runcommand
+    dispatch._runcommand = pagecmd