Don't install payload-pager at the module-level in zmqshell

The payload pager should be installed at shell instantiation, otherwise
any code that might import zmqshell that is not itself a kernel, will have broken page.page.

IPython/zmq/zmqshell.py

@@ -44,12 +44,6 b' from IPython.zmq.displayhook import ZMQShellDisplayHook, _encode_binary'
 from IPython.zmq.session import extract_header
 from session import Session
 
-#-----------------------------------------------------------------------------
-# Globals and side-effects
-#-----------------------------------------------------------------------------
-
-# Install the payload version of page.
-install_payload_page()
 
 #-----------------------------------------------------------------------------
 # Functions and classes
@@ -127,6 +121,9 b' class ZMQInteractiveShell(InteractiveShell):'
         env['PAGER'] = 'cat'
         env['GIT_PAGER'] = 'cat'
 
+        # And install the payload version of page.
+        install_payload_page()
+
     def auto_rewrite_input(self, cmd):
         """Called to show the auto-rewritten input for autocall and friends.