tests: demonstrate that pager.attend-<abbreviated> doesn't work stable

tests: demonstrate that pager.attend-<abbreviated> doesn't work

A pager.attend-* value that isn't a full command or alias name doesn't
work. We add explicit test coverage of this to demonstrate it.

--- a/tests/test-pager.t	Mon Apr 24 23:11:44 2017 -0700
+++ b/tests/test-pager.t	Tue Apr 25 00:19:03 2017 -0700
@@ -94,6 +94,14 @@
   paged! 'summary:     modify a 10\n'
   paged! '\n'
 
+Attend for an abbreviated command does not work
+
+  $ hg --config pager.attend-ident=true ident
+  46106edeeb38 tip
+
+  $ hg --config extensions.pager= --config pager.attend-ident=true ident
+  46106edeeb38 tip
+
 Pager should not start if stdout is not a tty.
 
   $ hg log -l1 -q --config ui.formatted=False