ui: add ignore-single-command functionality

This closes the last feature gap other than the attend list from the
extension. For now, I'm leaving the attend list in the extension,
because I'm unsure it has merit in a world where commands have been
updated to take advantage of the modern API.

hgext/pager.py

@@ -94,6 +94,12 b' def uisetup(ui):'
                     break
 
             if usepager:
+                # Slight hack: the attend list is supposed to override
+                # the ignore list for the pager extension, but the
+                # core code doesn't know about attend, so we have to
+                # lobotomize the ignore list so that the extension's
+                # behavior is preserved.
+                ui.setconfig('pager', 'ignore', '', 'pager')
                 ui.pager('extension-via-attend-' + cmd)
         return orig(ui, options, cmd, cmdfunc)
 

mercurial/ui.py

@@ -851,6 +851,7 b' class ui(object):'
         """
         if (self._neverpager
             or self.pageractive
+            or command in self.configlist('pager', 'ignore')
             # TODO: if we want to allow HGPLAINEXCEPT=pager,
             # formatted() will need some adjustment.
             or not self.formatted()