wrapfunction: use sysstr instead of bytes as argument in "pager"

This is as valid and simpler, it will help us to eventually get ride of
`safehasattr`.

hgext/pager.py

@@ -76,7 +76,7 b' def uisetup(ui):'
                 ui.disablepager()
         return orig(ui, options, cmd, cmdfunc)
 
-    extensions.wrapfunction(dispatch, b'_runcommand', pagecmd)
+    extensions.wrapfunction(dispatch, '_runcommand', pagecmd)
 
 
 attended = [b'annotate', b'cat', b'diff', b'export', b'glog', b'log', b'qdiff']